staging: dgap: fix returned errno code in dgap_parsefile()

The driver is using -1 instead of the -ENOMEM defined macro to specify
that a buffer allocation failed. Since the error number is propagated,
the caller will get a -EPERM which is the wrong error condition.

Also, the smatch tool complains with the following warning:

dgap_parsefile() warn: returning -1 instead of -ENOMEM is sloppy

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>