media: cx23885: check allocation return

Checking of kmalloc() seems to have been committed - as
cx23885_dvb_register() is checking for != 0 return, returning
-ENOMEM should be fine here.  While at it address the coccicheck
suggestion to move to kmemdup rather than using kmalloc+memcpy.

Fixes: 46b21bba ("[media] Add support for DViCO FusionHDTV DVB-T Dual Express2")

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>