ImmersiveDesktop: fix potential arrayoutofbounds index with 'smartsummary'

final string strValueMode is set before setImmersiveModeEntries() modifies the
available entries in the listpreference array.  After setImmersiveModeEntries()
is called smartsummary uses strValueMode to set the summary.

Change-Id: I64b6032d809bb1f442a085c70f93e61b827bdb41
Merge "ImmersiveDesktop: fix potential arrayoutofbounds index with 'smartsummary'" into kk44