loader: Fix leak of kernel driver name
This is strdup'd, it needs to be freed. CID: 1458032 Fixes: f93bb2fb ("loader: Check if the kernel driver is i915 before loading iris") Reviewed-by:Eric Engestrom <eric@engestrom.ch> Reviewed-by:
Sagar Ghuge <sagar.ghuge@intel.com> Tested-by: Marge Bot <mesa/mesa!3630> Part-of: <mesa/mesa!3630>