[media] ov2640: Propagate the real error on devm_clk_get() failure

devm_clk_get() may return different error codes other than -EPROBE_DEFER,
so it is better to return the real error code instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>