serial: sc16is7xx: fix implicit decl of func copy_{to,from}_user

Fix by including linux/uaccess.h:

   drivers/tty/serial/sc16is7xx.c: In function 'sc16is7xx_ioctl':
>> drivers/tty/serial/sc16is7xx.c:861:3: error: implicit declaration of function 'copy_from_user' [-Werror=implicit-function-declaration]
>> drivers/tty/serial/sc16is7xx.c:867:3: error: implicit declaration of function 'copy_to_user' [-Werror=implicit-function-declaration]

Signed-off-by: Jon Ringle <jringle@gridpoint.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>