drm/amdgpu: Fix potential out-of-bounds access in 'amdgpu_discovery_reg_base_init()'

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: Fix potential out-of-bounds access in 'amdgpu_discovery_reg_base_init()' The issue arises when the array 'adev->vcn.vcn_config' is accessed before checking if the index 'adev->vcn.num_vcn_inst' is within the bounds of the array. The fix involves moving the bounds check before the array access. This ensures that 'adev->vcn.num_vcn_inst' is within the bounds of the array before it is used as an index. Fixes the below: drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1289 amdgpu_discovery_reg_base_init() error: testing array offset 'adev->vcn.num_vcn_inst' after use.