core: ofnode: Fix mem leak in error path

A newly created property is currently not freed if a name could not be
allocated. This patch fixes the resulting memory leak in the error
patch.

Reported-by: Coverity (CID: 184085)
Fixes: e369e58d ("core: Add functions to set properties in live-tree")
Signed-off-by: Mario Six <mario.six@gdsys.cc>