mfd: ucb1x00: Allow IRQ probing to work with IRQs > 32

probe_irq_on() only returns non-zero if it found any interrupts below
IRQ32 which could be probe candidates.  If all the probable interrupts
are higher than 32, then this will cause a failure.  Fix this.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>