msm: camera: req_mgr: Remove unwanted v4l2 operation

CCI hardware is no longer register as device node with v4l2 layer.
At time of notify message, there is missing check to read subdev
name, which cause the null pointer issue. This change removes
the sudbev node reading operation with devnode pointer as it is
not being use anywhere in functionality.

CRs-Fixed: 2702760, 2727771
Change-Id: Id362bd2edf4eea35f05115ae3a5b6c1d761bb437
Signed-off-by: Jigarkumar Zala <jzala@codeaurora.org>