swupdate-common: drop source parm from prepare-sw-description
swupdate-common: drop source parm from prepare-sw-description

Value can be easier extracted by reading from database.

Signed-off-by: Stefano Babic <2c2905e0c2877c7e4ce40c7425e972302953fda5@denx.de>

sbabic/meta-swupdate,sbabic/meta-swupdate