drivers: serial: nrfx_uart: fix pin disconnect in suspend when !PINCTRL

Fix pin disconnection when COFNIG_PINCTRL=n, so that less power is used
in suspended state. This seems to be a copy-paste kind of bug, since
when both resuming and suspending the same configuration was applied.

Fixes: 5567d7ae ("drivers: serial: nrfx_uart: add support for
  pinctrl")

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>