drm/amdgpu: Fix up missing kdoc parameter 'inst' in get_wave_count() & kgd_gfx_v9_get_cu_occupancy()

Fix these warnings by adding 'inst' arguments to kdocs.

gcc with W=1
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gfx_v9.c:692: warning: Function parameter or member 'inst' not described in 'get_wave_count'
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gfx_v9.c:763: warning: Function parameter or member 'inst' not described in 'kgd_gfx_v9_get_cu_occupancy'

Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>