update-rc.d.bbclass: add MLPREFIX when set RRECOMMENDS

update-rc.d.bbclass: add MLPREFIX when set RRECOMMENDS

Fixed when build with multilib:
WARNING: Multilib QA Issue: lib32-alsa-state package lib32-alsa-state - suspicious values 'update-rc.d' in RRECOMMENDS
WARNING: Multilib QA Issue: lib32-modutils-initscripts package lib32-modutils-initscripts - suspicious values 'update-rc.d' in RRECOMMENDS
WARNING: Multilib QA Issue: lib32-init-ifupdown package lib32-init-ifupdown - suspicious values 'update-rc.d' in RRECOMMENDS
WARNING: Multilib QA Issue: lib32-xserver-nodm-init package lib32-xserver-nodm-init - suspicious values 'update-rc.d' in RRECOMMENDS
WARNING: Multilib QA Issue: lib32-sysklogd package lib32-sysklogd - suspicious values 'update-rc.d' in RRECOMMENDS

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>