drm/amdgpu/userq: Do not allow userspace to trivially triger kernel warnings

In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu/userq: Do not allow userspace to trivially triger kernel warnings

Userspace can either deliberately pass in the too small num_fences, or the

required number can legitimately grow between the two calls to the userq

wait ioctl. In both cases we do not want the emit the kernel warning

backtrace since nothing is wrong with the kernel and userspace will simply

get an errno reported back. So lets simply drop the WARN_ONs.

(cherry picked from commit 2c333ea579de6cc20ea7bc50e9595ef72863e65c)