msm: camera: cdm: Decrement write-count only after Bl commit

After Hw Bl cmd write, we are decrementing write count.
Again after committing BL we are decrementing write count.
Due to this there is a chance of write count becoming -1 thus
leading to CDM overflow issue. Hence decrement write count
only after committing BL.

CRs-Fixed: 2768031
Change-Id: I8faf6ea7d5e9e34e1e034c89132ed131b4d6cafc
Signed-off-by: Shravya Samala <shravyas@codeaurora.org>