i965/vec4: Consider removal of no-op MOVs as progress during register coalesce.

Bug found by the liveness analysis validation pass that will be
introduced in a later commit.  The no-op MOV check in
opt_register_coalesce() was removing instructions which makes the
cached liveness analysis calculation inconsistent with the shader IR.
We were failing to set progress to true in that case though, which
means that invalidate_live_intervals() wouldn't necessarily be called
at the end of the function.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Matt Turner <mattst88@gmail.com>
(cherry picked from commit 7d7990cf65)

src/mesa/drivers/dri/i965/brw_vec4.cpp

@@ -1002,6 +1002,7 @@ vec4_visitor::opt_register_coalesce()
 
          if (is_nop_mov) {
             inst->remove(block);
+            progress = true;
             continue;
          }
       }