drivers: staging: ft1000: ft1000-usb: ft1000_debug.c: check return value of get_user...

drivers: staging: ft1000: ft1000-usb: ft1000_debug.c: check return value of get_user() in ft1000_ioctl()

get_user() may fail and cause 'msgsz' uninitialized, so need give a
check. The related warning (with allmodconfig under hexagon):

    CC [M]  drivers/staging/ft1000/ft1000-usb/ft1000_debug.o
  drivers/staging/ft1000/ft1000-usb/ft1000_debug.c: In function 'ft1000_ioctl':
  include/uapi/linux/swab.h:53:9: warning: 'msgsz' may be used uninitialized in this function [-Wuninitialized]
  drivers/staging/ft1000/ft1000-usb/ft1000_debug.c:533:17: note: 'msgsz' was declared here

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>