swupdate git define PV

The devtool workflow does not work without setting PV properly.

To prefer the git version add the following line to the distro config:
  PREFERRED_VERSION_swupdate = "2019.04+git%"

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>

recipes-support/swupdate/swupdate_git.bb

@@ -4,3 +4,4 @@ require swupdate_tools.inc
 DEFAULT_PREFERENCE = "-1"
 
 SRCREV ?= "a8d45381253838b34e4e035c065a1cdf429b1f09"
+PV = "2019.04+git${SRCPV}"