[media] lirc_imon: simplify error handling code

Instead of using a state machine and a switch with lots of
fall-trough, use gotos and cleanup the error handling loop.

That removes those two smatch warnings:
	drivers/staging/media/lirc/lirc_imon.c:933 imon_probe() warn: possible memory leak of 'context'
	drivers/staging/media/lirc/lirc_imon.c:933 imon_probe() warn: possible memory leak of 'driver'

And make the error handling code more standard.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>