OpenCL: Avoid potential buffer overflow in cmdutils_opencl.c

The opt_opencl_bench function copied the device name using strcpy without checking if the source string was larger.
This patch fixes this by replacing the strcpy with av_strlcpy, with the string copy size capped to the destination buffer size.

Signed-off-by: Maneesh Gupta <maneesh.gupta@amd.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
