ARM: dts: STiH407: Move pio20 node to fix kernel warning

cat /sys/kernel/debug/pinctrl/921f080.pin-controller-front1/pingroups
leads to the kernel warning:

[   86.083560] st-pinctrl 921f080.pin-controller-front1: failed to get pin(-517) name
[   86.091192] ------------[ cut here ]------------
[   86.095897] WARNING: CPU: 0 PID: 1579 at drivers/pinctrl/core.c:1414 pinctrl_groups_show+0x144/0x16c
[   86.105072] Modules linked in:
[   86.108127] CPU: 0 PID: 1579 Comm: cat Tainted: G        W       4.6.0-00011-g9ba82e2-dirty #5
[   86.116728] Hardware name: STiH415/416 SoC with Flattened Device Tree
[   86.123194] [<c010fa90>] (unwind_backtrace) from [<c010bea8>] (show_stack+0x10/0x14)
[   86.130943] [<c010bea8>] (show_stack) from [<c038c5b0>] (dump_stack+0x98/0xac)
[   86.138167] [<c038c5b0>] (dump_stack) from [<c0129b58>] (__warn+0xe8/0x100)
[   86.145121] [<c0129b58>] (__warn) from [<c0129c20>] (warn_slowpath_null+0x20/0x28)
[   86.152681] [<c0129c20>] (warn_slowpath_null) from [<c03bf810>] (pinctrl_groups_show+0x144/0x16c)
[   86.161550] [<c03bf810>] (pinctrl_groups_show) from [<c0218a5c>] (seq_read+0x1ec/0x4c0)
[   86.169553] [<c0218a5c>] (seq_read) from [<c01f66f0>] (__vfs_read+0x20/0xd0)
[   86.176592] [<c01f66f0>] (__vfs_read) from [<c01f7414>] (vfs_read+0x7c/0x104)
[   86.183716] [<c01f7414>] (vfs_read) from [<c01f81a0>] (SyS_read+0x44/0x9c)
[   86.190585] [<c01f81a0>] (SyS_read) from [<c0108400>] (ret_fast_syscall+0x0/0x3c)
[   86.198158] ---[ end trace 1aa2e3ae820eeb3e ]---

Move the pincontroller pio20 node above the tsin4 node, which referred
to it, fix this warning.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Peter Griffin <peter.griffin@linaro.org>