kms: gracefully handle NULL save_state at cleanup
kms: gracefully handle NULL save_state at cleanup

If we failed to save any crtc state then we skip trying to restore the
old state at cleanup.

Reviewed-by: Neil Roberts <822ec91a7ef82248fd36162ca8ac3283eba70848@linux.intel.com>

djdeath/cogl,collects/cogl,djdeath/cogl-android,djdeath/cogl-android,Distrotech/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl-android,gcampax/cogl,Distrotech/cogl,collects/cogl,gcampax/cogl