broadcom/compiler: set current block on incrementing unifa

broadcom/compiler: set current block on incrementing unifa

When incrementing unifa address in DCE optimization, ensure that we
setup correctly the current block, so the ldfunif optimization is also
executed correctly.

This fixes
dEQP-VK.graphicsfuzz.cov-struct-float-array-mix-uniform-vectors
heap-buffer overflow with address sanitizer enabled.

v2 (Iago):
 - Save and restore current block

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12339>