[media] omap4iss: Don't check for DEBUG when printing IRQ debugging messages

Now that the VIDEO_OMAP4_DEBUG Kconfig option has been removed in favour
of dynamic printk, the DEBUG macro isn't defined anymore. Don't check
for it to guard IRQ debugging messages compilation, as they're already
guarded by the ISS_ISR_DEBUG macro.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>