mtd: mtdconcat: map: remove redundant assignment to variable 'size'

Variable 'size' is being assigned the value zero that will never be
read. The assignment is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/mtdconcat.c

···
 		size_t size, retsize;
 
 		if (to >= subdev->size) {
-			size = 0;
 			to -= subdev->size;
 			continue;
 		}