i965/vs: When failing due to lack of spilling, don't continue on.

Fixes assertion failure from double-free in oglc
glsl-arrayobject constructor.declaration.structure

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp

@@ -205,6 +205,7 @@ vec4_visitor::reg_allocate()
    if (!ra_allocate_no_spills(g)) {
       ralloc_free(g);
       fail("No register spilling support yet\n");
+      return;
    }
 
    /* Get the chosen virtual registers for each node, and map virtual