[media] saa7134: NEC scancode fix

This driver codes the two address bytes in reverse order when compared to the
other drivers, so make it consistent (and update the keymap, note that the
result is a prefix change from 0x6b86 -> 0x866b, and the latter is pretty
common among the NECX keymaps. While not conclusive, it's still a strong hint
that the change is correct).

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>