ibft: fix target info parsing in ibft module

I got this patch through Red Hat's bugzilla from the bug submitter and
patch creator.  I have just fixed it up so it applies without fuzz to
upstream kernels.

Original patch and description from Shyam kumar Iyer:

The issue [ibft module not displaying targets with short names] is because
of an offset calculatation error in the iscsi_ibft.c code.  Due to this
error directory structure for the target in /sys/firmware/ibft does not
get created and so the initiator is unable to connect to the target.

Note that this bug surfaced only with an name that had a short section at
the end.  eg: "iqn.1984-05.com.dell:dell".  It did not surface when the
iqn's had a longer section at the end.  eg:
"iqn.2001-04.com.example:storage.disk2.sys1.xyz"

So, the eot_offset was calculated such that an extra 48 bytes i.e.  the
size of the ibft_header which has already been accounted was subtracted
twice.

This was not evident with longer iqn names because they would overshoot
the tot...