pata: ixp4xx: Refer to cmd and ctl rather than csN

The two "cs0" and "cs1" are "chip selects" but on some
platforms such as GW2358 they are actually both in CS3
making this terminology very confusing. Call the
addresses "cmd" and "ctl" after function instead.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>