IB/iser: Add missing counter increment in iser_data_buf_aligned_len()

While adding sg chaining support to iSER, a "for" loop was replaced
with a "for_each_sg" loop. The "for" loop included the incrementation
of 2 variables. Only one of them is incremented in the current
"for_each_sg" loop. This caused iSER to think that all data is
unaligned, and all data was copied to aligned buffers.

This patch increments the missing counter inside the "for_each_sg"
loop whenever necessary.

Signed-off-by: Erez Zilber <erezz@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>