tty: serial: samsung: fixup accessors for endian

Fix the serial access code to deal with kernels built for big endian
operation.

Signed-off-by: Matthew Leach <matthew@mattleach.net>
Acked-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>