rtl8192se: Fix BUG caused by failure to check skb allocation

When downloading firmware into the device, the driver fails to check the
return when allocating an skb. When the allocation fails, a BUG can be
generated, as seen in https://bugzilla.redhat.com/show_bug.cgi?id=771656

.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>