uio_hv_generic: Fix another memory leak in error handling paths

In the Linux kernel, the following vulnerability has been resolved: uio_hv_generic: Fix another memory leak in error handling paths Memory allocated by 'vmbus_alloc_ring()' at the beginning of the probe function is never freed in the error handling path. Add the missing 'vmbus_free_ring()' call. Note that it is already freed in the .remove function.