ide: Correct IDE_BUS(dev) macro

The IDE_BUS(dev) macro was previously doing dev >> 1.  This however is a
mis-match of the usage in common/cmd_ide.c and would cause boards with
multiple ports / devices to not correctly detect all devices.  For more
details please see:
http://lists.denx.de/pipermail/u-boot/2012-April/122525.html



[Tom Rini: Reword commit message only]

Tested-by: Luka Perkov <uboot@lukaperkov.net>
Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
Signed-off-by: Tom Rini <trini@ti.com>