scsi: lpfc: Use int type to store negative error codes

Change the 'ret' variable in lpfc_sli4_issue_wqe() from uint32_t to int,
as it needs to store either negative error codes or zero returned by
lpfc_sli4_wq_put().

Storing the negative error codes in unsigned type, doesn't cause an
issue at runtime but can be confusing.  Additionally, assigning negative
error codes to unsigned type may trigger a GCC warning when the
-Wsign-conversion flag is enabled.

No effect on runtime.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Reviewed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>