of: be consistent in form of file mode

checkpatch whined about using S_IRUGO instead of octal equivalent
when adding phandle sysfs code, so used octal in that pending patch.
Change other instances of the S_* constants in the same file to
the octal form.

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>