bitbake: toasterui: fix version numbers for no PE specified

bitbake: toasterui: fix version numbers for no PE specified

PE is an optional field in recipes specifiying the epoch
for the recipe. The canonical form for the
full recipe version string is: PE:PV-PR

If no PE is specified, we shouldn't store the initial ":"
character, as it leads to inconsistency with how the
version string is used elsewhere. This patch drops the leading ":"

    [YOCTO #5459]

(Bitbake rev: f6031bd753917c459ab232d88d7dcfc3f10e8184)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>