iio: adc: cc10001: Fix the channel number mapping

When some of the ADC channels are reserved for remote CPUs,
the scan index and the corresponding channel number doesn't
match. This leads to convesion on the incorrect channel during
triggered capture.

Fix this by using a scan index to channel mapping encoded
in the iio_chan_spec for this purpose while starting conversion
on a particular ADC channel in trigger handler.

Also, the channel_map is not really used anywhere but in probe(), so
no need to keep track of it. Remove it from device structure.

While here, add 1 to number of channels to register timestamp channel
with the IIO core.

Fixes: 1664f6a5 ("iio: adc: Cosmic Circuits 10001 ADC driver")
Signed-off-by: Naidu Tellapati <naidu.tellapati@imgtec.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>