drivers: i2c_nrfx_twim: Fix compilation with disabled PINCTRL

This is a follow-up to commits 9974bb04
and 00ecc666.

Add one missing `#ifdef CONFIG_PINCTRL` and remove a no longer needed
one to restore the possibility to use this driver without PINCTRL.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>