mtd: spinand: winbond: Fix W35N number of planes/LUN

There's been a mistake when extracting the geometry of the W35N02 and
W35N04 chips from the datasheet. There is a single plane, however there
are respectively 2 and 4 LUNs. They are actually referred in the
datasheet as dies (equivalent of target), but as there is no die select
operation and the chips only feature a single configuration register for
the entire chip (instead of one per die), we can reasonably assume we
are talking about LUNs and not dies.

Reported-by: Andreas Dannenberg <dannenberg@ti.com>
Suggested-by: Vignesh Raghavendra <vigneshr@ti.com>
Fixes: 25e08bf6 ("mtd: spinand: winbond: Add support for W35N02JW and W35N04JW chips")
Cc: stable@vger.kernel.org
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>