drm/i915: fix up the relocate_entry refactoring

Somehow we've lost the error handling in the patch split-up between
the internal and external patch. This regression has been introduced
in

commit 5032d871f7d300aee10c309ea004eb4f851553fe
Author: Rafael Barbalho <rafael.barbalho@intel.com>
Date:   Wed Aug 21 17:10:51 2013 +0100

    drm/i915: Cleaning up the relocate entry function

This bug is exercised by igt/gem_reloc_vs_gpu/interruptible.

Cc: Rafael Barbalho <rafael.barbalho@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -310,6 +310,9 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	else
 		ret = relocate_entry_gtt(obj, reloc);
 
+	if (ret)
+		return ret;
+
 	/* and update the user's relocation entry */
 	reloc->presumed_offset = target_offset;