nir: Fix count when we didn't lower load_uniforms but did shift load_ubos.

nir: Fix count when we didn't lower load_uniforms but did shift load_ubos.

The fixed commit was really nice in mostly fixing num_ubos to reflect the
shader after lowering, but for
dEQP-GLES31.functional.compute.basic.ubo_to_ssbo_single_invocation there
are no default uniforms and so we skipped the increment, even though we
shifted the block index up.

Fixes: 4777ee1a62f0 ("nir: Always create UBO variable when lowering uniforms to ubo")
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4992>