pinctrl: single: fix offset management

The pinmux configuration DT node of a peripheral does not define a
physical address but an offset. Only by adding it to the base address of
the controller it is possible to calculate the physical address of the
register to be configured. Printing an offset also requires a different
formatting option than a physical address.

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