i2c: omap: always return IRQ_HANDLED

Always return IRQ_HANDLED otherwise we could get our IRQ line disabled due
to many spurious IRQs.

Signed-off-by: Felipe Balbi <balbi@ti.com>
[Trivial changes to commitlogs]
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>