tty: serial: samsung: return bool for s3c24xx_serial_txempty_nofifo()

tty: serial: samsung: return bool for s3c24xx_serial_txempty_nofifo()

s3c24xx_serial_txempty_nofifo() returned either 0 or BIT(2), which is
counterintuitive. Make the method return bool, and return true when TX
is empty and false otherwise.

Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://lore.kernel.org/r/20240119104526.1221243-15-tudor.ambarus@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>