tee: fix compiler warning in tee_shm_register()

Include <linux/uaccess.h> to avoid the warning:
   drivers/tee/tee_shm.c: In function 'tee_shm_register':
>> drivers/tee/tee_shm.c:242:14: error: implicit declaration of function 'access_ok' [-Werror=implicit-function-declaration]
     242 |         if (!access_ok((void __user *)addr, length))
         |              ^~~~~~~~~
   cc1: some warnings being treated as errors

Fixes: 573ae4f1 ("tee: add overflow check in register_shm_helper()")
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>