[media] ene_cir: get rid of warning: no previous prototype

drivers/media/rc/ene_ir.c:332:6: warning: no previous prototype for 'ene_rx_sense_carrier' [-Wmissing-prototypes]

Cc: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>