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