camera: Fix memory leak in HDR mode

The hdr YUV buffer counter should be incremented for every YUV
callback received.

b/18429991 Camera: ~40 MB memory leak per capture on N4 when using HDR mode

Change-Id: If90c931ebc9e87984bbe4b1d6f7934fd7f5daab9
Signed-off-by: Iliyan Malchev <malchev@google.com>