irqchip/keystone: Fix typo "sporious" -> "spurious"

Trivial fix to typo in dev_warn message.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lkml.kernel.org/r/20160901104454.26092-1-colin.king@canonical.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>