We can only have one page of data in each sg element, so we can not
cross a page boundary. Fail this case.

The 'while (len > 0 && data_len > 0) {}' loop is not necessary. The loop
can only be executed once.
Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>