spirv: fix retrieving dest type for OpFragmentMaskFetchAMD

spirv: fix retrieving dest type for OpFragmentMaskFetchAMD

Since the dest type is retrieved from the SPIR-V return type now,
we have to set it manually for OpFragmentMaskFetchAMD. The result
type must be a 32-bit unsigned integer type scalar.

Fix dEQP-VK.pipeline.multisample.shader_fragment_mask.* with RADV.

Fixes: a196f05fc22 ("nir/vtn: Use return type rather than image type for tex ops")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6533>