net: qlogic: Fix error paths in ql_alloc_large_buffers()

ql_alloc_large_buffers() has the usual RX buffer allocation
loop where it allocates skbs and maps them for DMA.  It also
treats failure as a fatal error.

There are (at least) three bugs in the error paths:

1. ql_free_large_buffers() assumes that the lrg_buf[] entry for the
first buffer that couldn't be allocated will have .skb == NULL.
But the qla_buf[] array is not zero-initialised.

2. ql_free_large_buffers() DMA-unmaps all skbs in lrg_buf[].  This is
incorrect for the last allocated skb, if DMA mapping failed.

3. Commit 1acb8f2a ("net: qlogic: Fix memory leak in
ql_alloc_large_buffers") added a direct call to dev_kfree_skb_any()
after the skb is recorded in lrg_buf[], so ql_free_large_buffers()
will double-free it.

The bugs are somewhat inter-twined, so fix them all at once:

* Clear each entry in qla_buf[] before attempting to allocate
  an skb for it.  This goes half-way to fixing bug 1.
* Set the .skb field only after the skb is DMA-mapped.  This
  fixes the rest.

Fixes: 1357bfcf ("qla3xxx: Dynamically size the rx buffer queue ...")
Fixes: 0f8ab89e ("qla3xxx: Check return code from pci_map_single() ...")
Fixes: 1acb8f2a

 ("net: qlogic: Fix memory leak in ql_alloc_large_buffers")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>