drm/amdgpu: Fix parameter annotations for VCN clock gating functions

The previous references to a non-existent `adev` parameter have been
removed & corrected to reflect the use of the `vinst` pointer, which
points to the VCN instance structure, in the below files:

- vcn_v1_0.c
- vcn_v2_0.c
- vcn_v3_0.c

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c:624: warning: Function parameter or struct member 'vinst' not described in 'vcn_v1_0_enable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c:624: warning: Excess function parameter 'adev' description in 'vcn_v1_0_enable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:376: warning: Function parameter or struct member 'vinst' not described in 'vcn_v2_0_mc_resume'
drivers/gpu/drm/amd/amdgpu/vcn_v2_0.c:376: warning: Excess function parameter 'adev' description in 'vcn_v2_0_mc_resume'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:776: warning: Function parameter or struct member 'vinst' not described in 'vcn_v3_0_disable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:776: warning: Excess function parameter 'adev' description in 'vcn_v3_0_disable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:776: warning: Excess function parameter 'inst' description in 'vcn_v3_0_disable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:965: warning: Function parameter or struct member 'vinst' not described in 'vcn_v3_0_enable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:965: warning: Excess function parameter 'adev' description in 'vcn_v3_0_enable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v3_0.c:965: warning: Excess function parameter 'inst' description in 'vcn_v3_0_enable_clock_gating'

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: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>