msm: camera: fd: Check detected faces limit

Max number of faces which can be detected in
face detection engine is 32. However we need to
handle cases when value from register is out of limit.

Change-Id: If6f93207d9a0720b3223bdb8fb224a0d081b4ee2
Signed-off-by: Gjorgji Rosikopulos <grosik@codeaurora.org>