package/qt5multimedia: fix install with gstreamer 0.10 and QT 5.6

package/qt5multimedia: fix install with gstreamer 0.10 and QT 5.6

QT 5.6 fails to correctly detect gstreamer support with gstreamer 0.10
as a result libqgsttools_p.so is not built and build fails on:
cp: cannot stat '/home/buildroot/autobuild/run/instance-1/output/host/xtensa-buildroot-linux-uclibc/sysroot/usr/lib/libqgsttools*.so.*': No such file or directory

Fixes:
 - http://autobuild.buildroot.org/results/c88afcd365418e29c89f247d9d887b5f786b0ec8

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>