Since kernel 4.16 the memory nodes got a @<reg> suffix so the fixup
won't work correctly anymore, because instead of adapting the extisting
one the fixup creates a new node and keeps the old (maybe incorrect)
node.

To be compatible with the old and new layout delete the found memory
node and create a new one. The new node follows the new @<reg> style.

The patch also renames the node parameter to make it clearer.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>