uio_hv_generic: Fix a memory leak in error handling paths

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

uio_hv_generic: Fix a memory leak in error handling paths

If 'vmbus_establish_gpadl()' fails, the (recv|send)_gpadl will not be

updated and 'hv_uio_cleanup()' in the error handling path will not be

able to free the corresponding buffer.

In such a case, we need to free the buffer explicitly.