net: mvpp2: fix the txq_init error path

When an allocation in the txq_init path fails, the allocated buffers
end-up being freed twice: in the txq_init error path, and in txq_deinit.
This lead to issues as txq_deinit would work on already freed memory
regions:

    kernel BUG at mm/slub.c:3915!
    Internal error: Oops - BUG: 0 [#1] PREEMPT SMP

This patch fixes this by removing the txq_init own error path, as the
txq_deinit function is always called on errors. This was introduced by
TSO as way more buffers are allocated.

Fixes: 186cd4d4

 ("net: mvpp2: software tso support")
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>