[lldb] [Process/FreeBSDRemote] Replace GetRegisterSetCount()

[mgorny]

Summary

Replace the wrong code in GetRegisterSetCount() with a constant return.
The original code passed register index in place of register set index,
effectively getting always true. Correcting the code to check for
register set existence is not possible as LLDB supports only eliminating
last register sets. Just return the full number for now which should
be NFC.

lldb/source/Plugins/Process/FreeBSDRemote/NativeRegisterContextFreeBSD_x86_64.cpp

NativeRegisterContextFreeBSD_x86_64::NativeRegisterContextFreeBSD_x86_64(
 
   for (int i : {FPRegSet, DBRegSet})
     m_regset_offsets[i] = GetRegisterInfoInterface()
                               .GetRegisterInfo()[first_regnos[i]]
                               .byte_offset;
 }
 
 uint32_t NativeRegisterContextFreeBSD_x86_64::GetRegisterSetCount() const {
-  uint32_t sets = 0;
-  for (uint32_t set_index = 0; set_index < k_num_register_sets; ++set_index) {
-    if (GetSetForNativeRegNum(set_index))
-      ++sets;
-  }
-
-  return sets;
+  return k_num_register_sets;
 }
 
 const RegisterSet *
 NativeRegisterContextFreeBSD_x86_64::GetRegisterSet(uint32_t set_index) const {
   switch (GetRegisterInfoInterface().GetTargetArchitecture().GetMachine()) {
   case llvm::Triple::x86:
     return &g_reg_sets_i386[set_index];
   case llvm::Triple::x86_64: