of/unittest: remove the duplicate of_changeset_init

Remove the duplicate of_changeset_init. In of_selftest_changeset
testcase, the "struct of_changeset chgset" is initialized twice,
but only once is enough. so, drop the first initializtion code.

Signed-off-by: Wang Long <long.wanglong@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>