[AMDGPU][MC] Restore old error position for "too few operands"

[scott.linder]

Summary

Revert part of https://reviews.llvm.org/D92084 to make it simpler to
start consuming the EndOfStatement token within AMDGPU's
ParseInstruction in a future patch. This also brings us back to what
every other target currently does.

A future change to move the position back to the end of the statement
would likely need to audit all of the AMDGPUOperand SMLoc ranges, and
determine the SMLoc for the last character of the last operand.

[dp]

LGTM. Thank you!

llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp

case Match_MissingFeature:
     // mnemonic is valid. A match was found but it requires
     // features which are not supported on this GPU.
     return Error(IDLoc, "operands are not valid for this GPU or mode");
 
   case Match_InvalidOperand: {
     SMLoc ErrorLoc = IDLoc;
     if (ErrorInfo != ~0ULL) {
       if (ErrorInfo >= Operands.size()) {
-        return Error(getLoc(), "too few operands for instruction");
+        return Error(IDLoc, "too few operands for instruction");
       }
       ErrorLoc = ((AMDGPUOperand &)*Operands[ErrorInfo]).getStartLoc();
       if (ErrorLoc == SMLoc())
         ErrorLoc = IDLoc;
     }
     return Error(ErrorLoc, "invalid operand for instruction");
   }
 

llvm/test/MC/AMDGPU/exp-err.s

 
 exp 0 v3, v2, v1, v0
 // GCN: :5: error: invalid operand for instruction
 
 exp , v3, v2, v1, v0
 // GCN: :5: error: unknown token in expression
 
 exp
-// GCN: :4: error: too few operands for instruction
+// GCN: :1: error: too few operands for instruction
 
 exp mrt0 s0, v0, v0, v0
 // GCN: 10: error: invalid operand for instruction
 
 exp mrt0 v0, s0, v0, v0
 // GCN: 14: error: invalid operand for instruction
 
 exp mrt0 v0, v0, s0, v0

llvm/test/MC/AMDGPU/gfx10_err_pos.s

 // CHECK-NEXT:{{^}}                       ^
 
 //==============================================================================
 // too few operands for instruction
 
 tbuffer_store_format_xyzw v[1:4], off, ttmp[4:7]
 // CHECK: error: too few operands for instruction
 // CHECK-NEXT:{{^}}tbuffer_store_format_xyzw v[1:4], off, ttmp[4:7]
-// CHECK-NEXT:{{^}}                                                ^
+// CHECK-NEXT:{{^}}^
 
 v_add_f32_e64 v0, v1
 // CHECK: error: too few operands for instruction
 // CHECK-NEXT:{{^}}v_add_f32_e64 v0, v1
-// CHECK-NEXT:{{^}}                    ^
+// CHECK-NEXT:{{^}}^
 
 //==============================================================================
 // too large value for expcnt
 
 s_waitcnt expcnt(8)
 // CHECK: error: too large value for expcnt
 // CHECK-NEXT:{{^}}s_waitcnt expcnt(8)
 // CHECK-NEXT:{{^}}                 ^