spirv/nir: tweak nir type when storage class is SpvStorageClassAtomicCounter

spirv/nir: tweak nir type when storage class is SpvStorageClassAtomicCounter

GLSL types differentiates uint from atomic uint. On SPIR-V the type is
uint, and the variable has a specific storage class. So we need to
tweak the type based on the storage class.

Ideally we would like to get the proper type at vtn_handle_type, but
we don't have the storage class at that moment.

We tweak only the nir type, as is the one that really requires it.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>