lib32-qt4-examples: fix QA warnings and INSANE_SKIP not work

lib32-qt4-examples: fix QA warnings and INSANE_SKIP not work

Fix the following warnings:
...
lib32-qt4-examples: found library in wrong location: /usr/bin/qt4/examples/tools/echoplugin/plugin/libechoplugin.so
lib32-qt4-examples: found library in wrong location: /usr/bin/qt4/examples/tools/plugandpaint/plugins/libpnp_extrafilters.so
...

In oe-core f119566477243ce43b727492dc78b9cb3dd76de4, it added INSANE_SKIP
libdir for examples packages as it includes plugin shared libraries outside
of libdir.

But it hardcoded ${QT_BASE_NAME} as INSANE_SKIP's package name
and it didn't work while multilib enabled.

Add ${MLPREFIX} as package name's prefix in INSANE_SKIP

[YOCTO #5516]

(From OE-Core rev: d63588ddd5a1f08fff90f5bb3f7278490e359720)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>