video: tegra: host: Fix channel refcount issues

video: tegra: host: Fix channel refcount issues

This patch fixes few possible races in channel initialisation and
deinitialisation:
- If two channel initialisations were running concurrently for
the same device and the first initialisation failed, we potentially
gave an uninitialised channel to the second requester
- If putchannel() triggered uninitialisation, we were still able
to give the channel in getchannel().

Bug 200013323

Change-Id: I99fa726db99fbb98401d5703cc2572131907f726
(cherry picked from commit 4fb20fef4a9eaf222c3f6d4c83fcb495f207c478)
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/498509
Reviewed-on: http://git-master/r/538725
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Shreshtha Sahu <ssahu@nvidia.com>
Tested-by: Shreshtha Sahu <ssahu@nvidia.com>
Reviewed-by: Venkat Moganty <vmoganty@nvidia.com>
Reviewed-by: Shridhar Rasal <srasal@nvidia.com>