drm/amd/amdgpu: enable W=1 for amdgpu

We have a clean build with W=1 as of
commit c168feed ("drm/amd/display/amdgpu_dm/amdgpu_dm_helpers: Move
SYNAPTICS_DEVICE_ID into CONFIG_DRM_AMD_DC_DCN ifdef"). So, let's enable
these checks unconditionally for the entire module to catch these errors
during development.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>