serial: samsung: enable clock before accessing interrupt mask resister

Ensure that the uart clock is enabled prior to writing to the
interrupt mask register in s3c24xx_serial_resume_noirq function.
Without enabing the uart clock, the uart register cannot be accessed.

Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>