drm/amdgpu: Fix up kdoc in sdma_v4_4_2.c

Address a bunch of kdoc warnings:

gcc with W=1
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:426: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_gfx_stop'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:457: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_rlc_stop'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:470: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_page_stop'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:506: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_ctx_switch_enable'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:794: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_rlc_resume'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:810: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_load_microcode'
drivers/gpu/drm/amd/amdgpu/sdma_v4_4_2.c:854: warning: Function parameter or member 'inst_mask' not described in 'sdma_v4_4_2_inst_start'

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>