ARM: topology: remove unneeded check for /cpus node

Checking for "/cpus" node is not necessary as of_get_cpu_node() will fail
later on anyways. The call to of_find_node_by_path() also leaks a
reference. So just remove the check.

Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>