arm/tegra: Fix section mismatch errors in tegra20 pinmux

tegra20_pinmux_init() is called from the pinmux's probe() function, and
hence should be __devinit not __init.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>