of: fdt: do not update local variable after use

Fix the below warning:
drivers/of/fdt.c:196:4: warning: Value stored to 'pprev' is never read
[clang-analyzer-deadcode.DeadStores]
             pprev      = &pp->next;
             ^            ~~~~~~~~~

Signed-off-by: Ohhoon Kwon <ohoono.kwon@samsung.com>
Link: https://lore.kernel.org/r/20210803101309.904-1-ohoono.kwon@samsung.com


Signed-off-by: Rob Herring <robh@kernel.org>