staging: rtl8188eu: Skip unnecessary field checks

Skip unnecessary request field checks when the information element
pointer is null.

Signed-off-by: Aymen Qader <qader.aymen@gmail.com>
ACKed-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>