broadcom/compiler: fix flags check for ldvary merge

We were checking that the previous instruction doesn't write flags,
but we also need to check it doesn't read them.

Fixes: 1784dd22a3 ('broadcom/compiler: pipeline smooth ldvary sequences')
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9431>

src/broadcom/compiler/qpu_schedule.c

@@ -1644,6 +1644,8 @@ fixup_pipelined_ldvary(struct v3d_compile *c,
          */
         if (v3d_qpu_writes_flags(&prev->qpu))
                 return false;
+        if (v3d_qpu_reads_flags(&prev->qpu))
+                return false;
 
         /* Move the ldvary to the previous instruction and remove it from the
          * current one.