Revert "serial: omap: Fix IRQ handling return value"

This reverts commit 908fd7e5.

Kevin writes:
	Greg, without a better justification in the changelog, I think
	this patch should be dropped from tty-next.

Reported-by: Kevin Hilman <khilman@linaro.org>
Cc: Ruchika Kharwar <ruchika@ti.com>
Cc: Alexander Savchenko <oleksandr.savchenko@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>