Modify the AM33XX_IOPAD macro so that it works now that #pinctrl-cells =
<2>. The third parameter is just a zero and the pinctrl-single driver
will just OR this with the second parameter so it has no actual effect.

There are no longer any dts files using this macro (following my patch
to am335x-guardian.dts), but this will keep dts files not in mainline
from breaking.

Fixes: 27c90e5e ("ARM: dts: am33xx-l4: change #pinctrl-cells from 1 to 2")
Suggested-by: Tony Lindgren <tony@atomide.com>
Reported-by: Trent Piepho <tpiepho@gmail.com>
Link: https://lore.kernel.org/linux-devicetree/20200921064707.GN7101@atomide.com/Signed-off-by: Drew Fustini <drew@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>