drivers: memc: don't check pin control return code

Some SOCs, such as the RT1064 and RT1024, use internal flash and don't
define pinmux settings for the flexspi. Don't check the return code of
pinctrl_apply_state, because the flexspi driver will fail to initialize
when the pin mux settings are simply not required.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>