qt5: factor Qt5 version

Since the Qt5 version will be the same for all Qt5 modules, factor it
in qt5/qt5.mk as QT5_VERSION.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/qt5/qt5.mk

@@ -1,3 +1,4 @@
+QT5_VERSION = 5.0.1
 include package/qt5/*/*.mk
 
 define QT5_LA_PRL_FILES_FIXUP

package/qt5/qt5base/qt5base.mk

@@ -4,7 +4,7 @@
 #
 #############################################################
 
-QT5BASE_VERSION = 5.0.1
+QT5BASE_VERSION = $(QT5_VERSION)
 QT5BASE_SITE = http://releases.qt-project.org/qt5/$(QT5BASE_VERSION)/submodules_tar/
 QT5BASE_SOURCE = qtbase-opensource-src-$(QT5BASE_VERSION).tar.xz