[MTD] ofpart: Check name property to determine partition nodes.

SLOF has a further node which could not be evaluated
by the current routine. The current routine returns
because the node hasn't the required reg property. As
fix this patch adds a check to determine the partition
child nodes. If the node is not a partition the number
of total partitions will be decreased and loop continues
with the next nodes.

Signed-off-by: Benjamin Krill <ben@codiert.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>