Use 5.5.1 branch for meta-qt5

5.5.1 branch has been rebased against upstream/master and
updated to use Qt 5.5.1

Change-Id: Ib575be637b44500848210d6ccb8c5456d1d5200e
Reviewed-by: aavit <eirik.aavitsland@theqtcompany.com>

scripts/manifest_qt5.xml

@@ -7,7 +7,7 @@
 
   <project name="meta-qt5"
            remote="playground"
-           revision="5.5-next"
+           revision="5.5.1"
            path="sources/meta-qt5"/>
 
 </manifest>