composer: Correct GetDisplayCapabilities return value

1. setToExternal requires caller to ensure that the underlying memory
   stays valid for the lifetime of this hidl_vec. But the current
   implementation assigns the capabilities from a local variable.
   Change this to populate the capabilities directly.
2. Remove redundant GetDisplayVsyncPeriod call in QtiComposerClient
   onVsync_2_4 function.

CRs-Fixed: 2669697
Change-Id: If2493376e7b2b134cf98d89d8d4c3109062673c7
3 files changed