qed: fix the allocation of the chains with an external PBL

Dan reports static checker warning:

"The patch 9b6ee3cf: "qed: sanitize PBL chains allocation" from Jul
23, 2020, leads to the following static checker warning:

	drivers/net/ethernet/qlogic/qed/qed_chain.c:299 qed_chain_alloc_pbl()
	error: uninitialized symbol 'pbl_virt'.

drivers/net/ethernet/qlogic/qed/qed_chain.c
   249  static int qed_chain_alloc_pbl(struct qed_dev *cdev, struct qed_chain *chain)
   250  {
   251          struct device *dev = &cdev->pdev->dev;
   252          struct addr_tbl_entry *addr_tbl;
   253          dma_addr_t phys, pbl_phys;
   254          __le64 *pbl_virt;
                ^^^^^^^^^^^^^^^^
[...]
   271          if (chain->b_external_pbl)
   272                  goto alloc_pages;
                        ^^^^^^^^^^^^^^^^ uninitialized
[...]
   298                  /* Fill the PBL table with the physical address of the page */
   299                  pbl_virt[i] = cpu_to_le64(phys);
                        ^^^^^^^^^^^
[...]
"

This issue was introduced with commit c3a321b0 ("qed: simplify
initialization of the chains with an external PBL"), when
chain->pbl_sp.table_virt initialization was moved up to
qed_chain_init_params().
Fix it by initializing pbl_virt with an already filled chain struct field.

Fixes: c3a321b0 ("qed: simplify initialization of the chains with an external PBL")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>