[NFC][AMDGPU] Mark C code in AMDGPUUsage.rst

[foad]

Looks obvious.

llvm/docs/AMDGPUUsage.rst

.. table:: AMDGPU Code Object V2 ELF Note Record Enumeration Values
      ``NT_AMD_HSA_METADATA``               10
      ``NT_AMD_HSA_ISA_NAME``               11
      ===================================== =====
 
 ``NT_AMD_HSA_CODE_OBJECT_VERSION``
   Specifies the code object version number. The description field has the
   following layout:
 
-  .. code::
+  .. code:: c
 
     struct amdgpu_hsa_note_code_object_version_s {
       uint32_t major_version;
       uint32_t minor_version;
     };
 
   The ``major_version`` has a value less than or equal to 2.
 
 ``NT_AMD_HSA_HSAIL``
   Specifies the HSAIL properties used by the HSAIL Finalizer. The description
   field has the following layout:
 
-  .. code::
+  .. code:: c
 
     struct amdgpu_hsa_note_hsail_s {
       uint32_t hsail_major_version;
       uint32_t hsail_minor_version;
       uint8_t profile;
       uint8_t machine_model;
       uint8_t default_float_round;
     };
 
 ``NT_AMD_HSA_ISA_VERSION``
   Specifies the target ISA version. The description field has the following layout:
 
-  .. code::
+  .. code:: c
 
     struct amdgpu_hsa_note_isa_s {
       uint16_t vendor_name_size;
       uint16_t architecture_name_size;
       uint32_t major;
       uint32_t minor;
       uint32_t stepping;
       char vendor_and_architecture_name[1];