platform: msm_shared: Do not reset success bit for alternate slot

When the current slot becomes unbootable, it switches to alternate slot
and during the switch, all the partition attributes are reset. This can
lead to issues of making both slots unbootable when other sequences impacting
device bootup are initiated.

So, reset the attributes only when the slot is switched through fastboot
command and retain the SUCCESS bit when slot switch happens due to
unbootable current slot

Change-Id: If9a5eb5284035bdfce09b2114cebedd65100f896