mrf24j40: remove trailing semicolon

This patch removes a trailing semicolon which was introduced by commit
d3f1bc3 ("mrf24j40: add cca mode support") and reported by kbuild test
robot.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>