msm: camera: core: Prevent crash on kref_put

kref_put causes crash if refcount is zero.
This change prevents crash by checking if refcount value.

CRs-Fixed: 2553290
Change-Id: Ie9a950b289cdb2b8fca8c5d025be540d926eadbd
Signed-off-by: Trishansh Bhardwaj <tbhardwa@codeaurora.org>