iscsi_ibft: Fix finding Broadcom specific ibft sign

iscsi_ibft: Fix finding Broadcom specific ibft sign

commit 629c27aa0c930b9c67188cfc625bf6cdd2af6764 upstream.

Search for Broadcom specific ibft sign "BIFT"
along with other possible values on UEFI

This patch is fix for regression introduced in
“935a9fee51c945b8942be2d7b4bae069167b4886”.
https://lkml.org/lkml/2011/12/16/353

This impacts Broadcom CNA for iSCSI Boot on UEFI platform.

Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>