mtd: parser: imagetag: fix error codes in bcm963xx_parse_imagetag_partitions()

If the kstrtouint() calls fail, then this should return a negative
error code but it currently returns success.

Fixes: dd84cb022b31 ("mtd: bcm63xxpart: move imagetag parsing to its own parser")
Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/YBKFtNaFHGYBj+u4@mwanda

drivers/mtd/parsers/parser_imagetag.c

···
 			pr_err("invalid rootfs address: %*ph\n",
 				(int)sizeof(buf->flash_image_start),
 				buf->flash_image_start);
+			ret = -EINVAL;
 			goto out;
 		}
 
···
 			pr_err("invalid kernel address: %*ph\n",
 				(int)sizeof(buf->kernel_address),
 				buf->kernel_address);
+			ret = -EINVAL;
 			goto out;
 		}
 
···
 			pr_err("invalid kernel length: %*ph\n",
 				(int)sizeof(buf->kernel_length),
 				buf->kernel_length);
+			ret = -EINVAL;
 			goto out;
 		}
 
···
 			pr_err("invalid total length: %*ph\n",
 				(int)sizeof(buf->total_length),
 				buf->total_length);
+			ret = -EINVAL;
 			goto out;
 		}