staging: dgap: cleanup print messages for dgap driver

* use dev_{warn,err} instead of pr_{warn,err}
* removes dgap_err() and just use pr_err(). pr_err() used in
dgap_parsefile() not dev_err() because if dgap_parsefile() is
failed, just one message is printed.
* removes "out of memory" messages.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>