drm/radeon: don't check mipmap alignment if MIP_ADDRESS is FMASK

The MIP_ADDRESS state has 2 meanings. If the texture has one sample
per pixel, it's a pointer to the mipmap chain. If the texture has
multiple samples per pixel, it's a pointer to FMASK, a metadata buffer
needed for reading compressed MSAA textures. The mipmap
alignment rules do not apply to FMASK.

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>