mtd: mtdcore: constify name param in mtd_bdi_init

The bdi name is not modified by the function, it should be const.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210225143329.430012-1-tomas.winkler@intel.com