[PORT FROM R2] atomisp: optimize atomisp_acc_get_fw/index() to satisfy klockwork

[PORT FROM R2] atomisp: optimize atomisp_acc_get_fw/index() to satisfy klockwork

BZ: 17272

Due to a (not well optimized) logic Klockwork doesn't understand, it is
complaining about possible memory leak. This patch changes/optimizes
this logic to make Klockwork happier.

Change-Id: Ife10eb9f0aec2a164b93f28d29ae0a72c62e7bc6
Orig-Change-Id: Ie303427f4d16486f268940745b73692fa5d781f8
Signed-off-by: David Cohen <david.a.cohen@intel.com>
Reviewed-on: http://android.intel.com:8080/23490
Reviewed-by: Wang, Wen W <wen.w.wang@intel.com>
Reviewed-by: Zhang, Xiaolin <xiaolin.zhang@intel.com>
Reviewed-by: Hu, Gang A <gang.a.hu@intel.com>
Reviewed-by: Koskinen, Ilkka <ilkka.koskinen@intel.com>
Tested-by: Koski, Anttu <anttu.koski@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>
Reviewed-on: http://android.intel.com:8080/27993
Reviewed-by: Tuominen, TeemuX <teemux.tuominen@intel.com>
Reviewed-by: Koski, Anttu <anttu.koski@intel.com>