drm/i915/gem: Fix oops in error handling code

This code will Oops when it tries to i915_gem_object_free(obj) because
"obj" is an error pointer.

Fixes: 97d55396 ("drm/i915/region: convert object_create into object_init")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/YA6FkPn5S4ZDUGxq@mwanda


(cherry picked from commit ad8db423a30f0ac39a5483dfd726058135ff2bd2)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>