camera: Clarify docs for ICameraDeviceSession.repeatingRequestEnd()

The frame number being passed into the
ICameraDeviceSession.repeatingRequestEnd() call is the latest
frame number at which repeating requests will end. It is possible that
a repating request ends before this frame number due to requests being
cancelled, for instance, when the client abandons its bufferQueue.

Bug: 341021865

Test: build

Flag: DOCS_ONLY

Change-Id: Ib7f140f1dc6f449d5170a373ad24b863715c76ee
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>