Fix build when MFD_CROS_EC is not enabled but COMPILE_TEST=y.
Fixes this build error:

ERROR: "cros_ec_cmd_xfer_status" [drivers/media/platform/cros-ec-cec/cros-ec-cec.ko] undefined!
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>