scsi: qedi: remove declaration of nvm_image from stack

The nvm_image is a large struct qedi_nvm_iscsi_image object of over 24K so
don't declare it on the stack just for a sizeof requirement; use sizeof on
struct qedi_nvm_iscsi_image instead.

Fixes: c77a2fa3 ("scsi: qedi: Add the CRC size within iSCSI NVM image")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Manish Rangankar <mrangankar@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>