drm/amdgpu: Fix 32bit x86 compilation warning

drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c:187:2: warning: right shift count >= width of type [enabled by default]
drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c:173:2: warning: right shift count >= width of type [enabled by default]
drivers/gpu/drm/amd/amdgpu/vega10_ih.c:106:3: warning: right shift count >= width of type [enabled by default]

v2: Add a space between "&" and "0xff"

Reported by: kbuild-all@01.org

Signed-off-by: Alex Xie <AlexBin.Xie@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>