salt: use stable commit as source revision
salt: use stable commit as source revision

The salt recipe is out of development and should be taken off of AUTOREV
to reduce release burden. Staple the recipe to the current HEAD of the
ni/master/2018.3 branch - which seems to be reasonably stable.

Signed-off-by: Alex Stewart <04cdb2793e4fb0120cc30d1c823099f3862701f4@ni.com>
Acked-by: Rares Pop <d9574b758dce7f8f35eefd365cd2a75dda907696@ni.com>
Natinst-ReviewBoard-ID: 282176

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt