mtd: rawnand: intel: Remove undocumented compatible string

The "intel,nand-controller" compatible string is not part of the
dt-bindings. Remove it from the driver as it's not supposed to be used
without any documentation for it.

Fixes: 0b1039f0

 ("mtd: rawnand: Add NAND controller support on Intel LGM SoC")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220702231227.1579176-5-martin.blumenstingl@googlemail.com