'exit' functions should be marked as __exit, not __init.

Fixes: c10b1332 ("tty: serial: Add RDA8810PL UART driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/20190910041702.7357-1-christophe.jaillet@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>