Revert "Remove channel parameter from smd_[start|end]_scan"

This reverts commit ab306125208d447ec618e6354000549095eb1f93.
Remove channel parameter from smd_[start|end]_scan

The channel parameter was never necessary and removing it inline with
some cleanups.

Signed-off-by: Olof Johansson <dev@skyshaper.net>
Merge pull request #77 from Coi-l/separate

Fix signed-off