msm: cam: sync: Correctly calculate remaining count

When merging multiple sync objects, make sure only
active sync objects are counted towards the remaining
count. Do this so that the signaling logic for merged
objects is correct. Otherwise, the merged object will
never be signaled when all its children are signaled.

Change-Id: I2f3505bafd158ffd3ac17bfe7c1b8d714a7d0b96
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>