pinctrl: single: fix debug messages formatting

The dev_dbg(dev, "  reg/val 0x%pa/0x%08x\n", &reg, val); prints the 'reg'
address preceded by the prefix 0x0x instead of 0x. This because the
printf '%pa' format specifier already prepends the prefix '0x' to the
address displayed.

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