V4L/DVB (5448): M920x: rename megasky_identify_state to m920x_identify_state

This function should work for all m920x-based devices.

Signed-off-by: Aapo Tahkola <aet@rasterburn.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>