nir/linker: Fill the uniform's BLOCK_INDEX

nir/linker: Fill the uniform's BLOCK_INDEX

Binding comparison is used to determine the block the uniform is part
of. Note that to do the binding comparison we need the information in
UniformBlocks[] and ShaderStorageBlocks[] to be available, so we have
to call gl_nir_link_uniform_blocks() before linking the uniforms.

v2: add missing break (Timothy)

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