media: rc: rename s_learning_mode() to s_wideband_receiver()

The s_learning_mode() function is called in response to the ioctl
LIRC_SET_WIDEBAND_RECEIVER, so rename it to s_wideband_receiver().

Learning mode is when both the wideband receiver is turned on and
carrier reports are enabled.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>