mtd: parsers: ofpart: call of_node_get() for dedicated subpartitions

In order to parse sub-partitions, add_mtd_partitions() calls
parse_mtd_partitions() for all previously found partitions.

Each partition will end up being passed to parse_fixed_partitions(), and
its of_node will be treated as the ofpart_node.

Commit 7cce81df ("mtd: parsers: ofpart: fix OF node refcount leak in
parse_fixed_partitions()") added of_node_put() calls for ofpart_node on
all exit paths.

In the case where the partition passed to parse_fixed_partitions() has a
parent, it is treated as a dedicated partitions node, and of_node_put()
is wrongly called for it, even if of_node_get() was not called
explicitly.

On repeated bind / unbinds of the MTD, the extra of_node_put() ends up
decrementing the refcount down to 0, which should never happen,
resulting in the following error:

OF: ERROR: of_node_release() detected bad of_node_put() on
/soc/spi@80007000/flash@0/partitions/partition@0

Call of_node_get() to balance the call to of_node_put() done for
dedicated partitions nodes.

Fixes: 7cce81df ("mtd: parsers: ofpart: fix OF node refcount leak in parse_fixed_partitions()")
Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Tested-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>