staging: r8188eu: Fix smatch warning in os_dep/ioctl_linux.c

Smatch reports the following:
drivers/staging/rtl8188eu/os_dep/ioctl_linux.c:4891 set_group_key() warn: missing break? reassigning 'keylen'

As it suggests, there is a missing break statement.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>