scsi: qedi: Staticify non-external function 'qedi_get_iscsi_error'

Fixes the following W=1 kernel build warning(s):

 drivers/scsi/qedi/qedi_iscsi.c:1549:7: warning: no previous prototype for ‘qedi_get_iscsi_error’ [-Wmissing-prototypes]

Link: https://lore.kernel.org/r/20200723122446.1329773-38-lee.jones@linaro.org
Cc: QLogic-Storage-Upstream@cavium.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qedi/qedi_iscsi.c

@@ -1546,7 +1546,7 @@ static const struct {
 	},
 };
 
-char *qedi_get_iscsi_error(enum iscsi_error_types err_code)
+static char *qedi_get_iscsi_error(enum iscsi_error_types err_code)
 {
 	int i;
 	char *msg = NULL;