ns16550: Fix mem mapped endian check

Do a explicit check for CONFIG_SYS_BIG_ENDIAN and
CONFIG_SYS_LITTLE_ENDIAN to avoid errors on platforms where both
are undefined (x86).

Signed-off-by: Bernhard Messerklinger <bernhard.messerklinger@br-automation.com>
Reviewed-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
1 file changed