mime.bbclass: fix do_package_qa_multilib error of lib32-fltk

mime.bbclass: fix do_package_qa_multilib error of lib32-fltk

fltk.bb inherit mime.bbclass, mime.bbclass add RDEPEND during
populate_package, so need add mlprefix manually.

ERROR: QA Issue: lib32-fltk package lib32-fltk-dev - suspicious
values 'shared-mime-info-data-dev' in RRECOMMENDS [multilib]
ERROR: QA Issue: lib32-fltk package lib32-fltk-bin - suspicious
values 'shared-mime-info-data' in RDEPENDS [multilib]

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>