mtd: remove redundant assignment to pointer eb

Pointer eb is being assigned a value that is never read, the assignment
is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200911102321.22515-1-colin.king@canonical.com