lpfc: Fix return value of board_mode store

lpfc: Fix return value of board_mode store

[backport of b18f2a8765fc072701452f710ac164d243ee4579]
From: rkennedy <dick.kennedy@avagotech.com>

Orabug: 26439257

On hbacmd reset failure, observing wrong string "nline" in kernel log.

On failure, non negative value (1) is returned from sysfs store
routine. It is interpreted as count by kernel and store routine is
called again with the remaining characters as input.

Fix: Return negative error code (-EIO) in case of failure.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>