pinctrl: single: fix the loop counter variable type

The 'n' variable is used as a loop counter, not as a physical address,
and is used in a comparison with an int. So it makes sense to change
its type from phys_addr_t to int.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>