The return value of of_get_property() isn't checked before it is passed
to the strstr() function, if it happens that the return value is null
then this will result in a null pointer being dereferenced.

Add a check to see if the return value of of_get_property() is null and
if it is continue straight on to the next node.
Signed-off-by: NSuraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: NChris Smart <chris@distroguy.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>