ARM: integrator: fix OF-related regression

ARM: integrator: fix OF-related regression

Commit d8a3c81870002a53bdbace5a769367191992cc7a
"of: Ensure unique names without sacrificing determinism"
caused a boot failure regression on the Integrator machines.

The problem is probably caused by fiddling too much with
the device tree population in the OF init function, such
as passing the SoC bus device as parent when populating
the device tree.

This patch fixes the problem by:

- Avoiding to explicitly look up the tree root
- Look up devices needed before device population from
  the match only, passing NULL as root
- Passing NULL as root and parent when calling
  of_platform_populate()

After this the Integrators boot again. Tested on
Integrator/AP and Integrator/CP.

Cc: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>