tty: n_gsm: Add compat_ioctl

To use this driver with 32 bit userspace applications on 64 bit
kernels a compat_ioctl is needed.

Signed-off-by: Lars Poeschel <poeschel@lemonage.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>