drivers: net: cpsw: Fix broken loop condition in switch mode

0d961b3b (drivers: net: cpsw: fix buggy
loop condition) accidentally fixed a loop comparison in too many places
while fixing a real bug.

It was correct to fix the dual_emac mode section since there 'i' is used
as an index into priv->slaves which is a 0 based array.

However the other two changes (which are only used in switch mode)
are wrong since there 'i' is actually the ALE port number, and port 0
is the host port, while port 1 and up are the slave ports.

Putting the loop condition back in the switch mode section fixes it.

A comment has been added to point out the intent clearly to avoid future
confusion.  Also a comment is fixed that said the opposite of what was
actually happening.

Signed-off-by: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>