drm/amdgpu: remove excess function parameter description

Fixes gcc warning:

drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c:431: warning: Excess function
parameter 'sw' description in 'vcn_v2_5_disable_clock_gating'
drivers/gpu/drm/amd/amdgpu/vcn_v2_5.c:550: warning: Excess function
parameter 'sw' description in 'vcn_v2_5_enable_clock_gating'

Fixes: cbead2bd ("drm/amdgpu: add VCN2.5 VCPU start and stop")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>