V4L/DVB: ir-core-priv: fix a typo for RC6 config option

As Adreas pointed, RC6 should use CONFIG_IR_RC6_DECODER_MODULE, instead
of the RC5 config option.

Thanks-to: Andreas Oberitter <obi@linuxtv.org>
Acked-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>