msm: camera: Fix kernel overwrite GET_BUF_BY_IDX ioctl

Assign address of buf_info into ioctl_ptr.
Previously we were copying first 8 bytes of buf_info (content)
into ioctl_ptr. Which is dereferenced and written later causing
kernel overwrite vulnerability.

Change-Id: Ie5deae249da8208523027f8ec5632f960757e9bd
Signed-off-by: Trishansh Bhardwaj <tbhardwa@codeaurora.org>