pinctrl: rza1: Remove unneeded spinlock acquisitions

rza1_get_bit() is just a single register read.  Hence there's no need to
synchronize it with other register writes to the same bank.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Jacopo Mondi <jacopo@jmondi.org>