serial: samsung.c: mark s3c24xx_serial_remove as __devexit

Mark the remove function as __devexit so it gets eliminated in
CONFIG_HOTPLUG=n builds.  Saves ~100 bytes.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>