mtd: phram: Fix error return code in phram_setup()

Return a negative error code from the error handling case instead
of 0, as done elsewhere in this function.

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Yu Kuai <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/devices/phram.c

···
 	if (len == 0 || erasesize == 0 || erasesize > len
 	    || erasesize > UINT_MAX || rem) {
 		parse_err("illegal erasesize or len\n");
+		ret = -EINVAL;
 		goto error;
 	}