tee: optee: Pass a pointer to virt_addr_valid()

A pointer into virtual memory is represented by a (void *)
not an u32, so the compiler warns:

drivers/tee/optee/call.c:365:29: warning: passing argument 1
  of 'virt_to_pfn' makes pointer from integer without a
  cast [-Wint-conversion]

Fix this with an explicit cast.

Cc: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
[jw: fixed merge conflict]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>