[SCSI] iscsi_tcp: change & to &&

This change is basically a clean up.

datadgst_en is an int which comes from the user.  I didn't see anything
limiting it to 1 and 0 although obviously that's what it's supposed to
be.  If the user passed in 2 this test would fail.

This same if condition is repeated in another function and it uses &&
there.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>