soc/tegra: Fix bad of_node_put() in powergate init

soc/tegra: Fix bad of_node_put() in powergate init

The for_each_child_of_node macro itself maintains the correct reference
count of the nodes so the explicit of_node_put() call causes a warning:

[    0.098960] OF: ERROR: Bad of_node_put() on /pmc@7000e400/powergates/xusba
[    0.098981] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.11.3 #1-NixOS
[    0.098996] Hardware name: NVIDIA Jetson TX1 Developer Kit (DT)
[    0.099011] Call trace:
[    0.099034] [<ffff00000808a048>] dump_backtrace+0x0/0x2a0
[    0.099051] [<ffff00000808a30c>] show_stack+0x24/0x30
[    0.099069] [<ffff0000084a6494>] dump_stack+0x9c/0xc0
[    0.099090] [<ffff000008992214>] of_node_release+0xa4/0xa8
[    0.099107] [<ffff0000084a9270>] kobject_put+0x90/0x1f8
[    0.099124] [<ffff0000089914ac>] of_node_put+0x24/0x30
[    0.099140] [<ffff00000898cec4>] __of_get_next_child+0x4c/0x70
[    0.099155] [<ffff00000898cf28>] of_get_next_child+0x40/0x68
[    0.099173] [<ffff0000090a099c>] tegra_pmc_early_init+0x4e8/0x5ac
[    0.099189] [<ffff00000808399c>] do_one_initcall+0x5c/0x168
[    0.099206] [<ffff000009050c98>] kernel_init_freeable+0xd4/0x240
[    0.099224] [<ffff000008b2d658>] kernel_init+0x18/0x108
[    0.099238] [<ffff0000080836c0>] ret_from_fork+0x10/0x50

(It's not very apparent from the OF documentation that of_node_put() is
not needed; the macro itself has no docstring and of_get_next_child()
used in the implementation begins with "Returns a node pointer with
refcount incremented" but then only at the very end of the docstring
the crucial part "Decrements the refcount of prev" is mentioned.)

Fixes: a38045121bf42 ("soc/tegra: pmc: Add generic PM domain support")
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Signed-off-by: Thierry Reding <treding@nvidia.com>