mtd: mchp23k256: drop unneeded MODULE_ALIAS

The ID table already has respective entry and MODULE_DEVICE_TABLE and
creates proper alias for SPI driver.  Having another MODULE_ALIAS causes
the alias to be duplicated.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240414154943.127079-1-krzk@kernel.org