tty: serial: efm32: fix spelling mistake "reserverd" -> "reserved"

Fix a spelling mistake in a comment.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20200214141406.20792-1-alexandre.belloni@bootlin.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>