staging: rtl8712: remove unneeded NULL check

We knew "peventbuf" was a valid pointer and "peventbuf + 2" is also
non-NULL.  I have removed the check.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>