drm/i915/selftest/buddy: fixup igt_buddy_alloc_range

Dan reported the following static checker warning:

drivers/gpu/drm/i915/selftests/i915_buddy.c:670 igt_buddy_alloc_range()
error: we previously assumed 'block' could be null (see line 665)
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NMatthew Auld <matthew.auld@intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190815103210.11802-1-matthew.auld@intel.com

drivers/gpu/drm/i915/selftests/i915_buddy.c

@@ -665,6 +665,7 @@ static int igt_buddy_alloc_range(void *arg)
 		if (!block) {
 			pr_err("alloc_range has no blocks\n");
 			err = -EINVAL;
+			break;
 		}
 
 		if (i915_buddy_block_offset(block) != offset) {