mtd: spi-nor: cqspi: remove duplicate const

The variable was already marked 'const' before the previous
patch, but the qualifier was in an unusual place, and now the
extra 'const' causes a harmless warning:

drivers/mtd/spi-nor/cadence-quadspi.c:1286:34: error: duplicate 'const' declaration specifier [-Werror=duplicate-decl-specifier]

This removes the other 'const' instead.

Fixes: f993c123

 ("mtd: spi-nor: cqspi: make of_device_ids const")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>