clocksource/drivers/npcm: Fix misuse of GENMASK macro

Arguments are supposed to be ordered high then low.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/d6a9d49c9837d38816b71d783f5aed7235e8ca94.1562734889.git.joe@perches.com