staging: et131x: fix allocation failures

staging: et131x: fix allocation failures

We should check the ring allocations don't fail.
If we get a fail we need to clean up properly. The allocator assumes the
deallocator will be used on failure, but it isn't. Make sure the
right deallocator is always called and add a missing check against
fbr allocation failure.

[v2]: Correct check logic

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>