msm: camera: reqmgr: Reset previous skipped slot if valid request

It makes sure that last applied index also get reset when it is
modified with new index.

Change-Id: I47f717886e8a5287c4488fe9cfd91542fe733386
Signed-off-by: Tejas Prajapati <tpraja@codeaurora.org>
Signed-off-by: Alok Pandey <akumarpa@codeaurora.org>