drm: Use sizet type for len variable in drmcopy_field()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.9.331 by commit 12753d7a2cebca5affd9298ae17cfab950e64f5d. For more details please see the references link.