dm: Convert to use ERR_CAST()

Use ERR_CAST() as it is designed for casting an error pointer to
another type.

This macro utilizes the __force and __must_check modifiers, which instruct
the compiler to verify for errors at the locations where it is employed.
Signed-off-by: Yuesong Li <liyuesong@vivo.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

drivers/md/dm-thin.c

@@ -2948,7 +2948,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
 	pmd = dm_pool_metadata_open(metadata_dev, block_size, format_device);
 	if (IS_ERR(pmd)) {
 		*error = "Error creating metadata object";
-		return (struct pool *)pmd;
+		return ERR_CAST(pmd);
 	}
 
 	pool = kzalloc(sizeof(*pool), GFP_KERNEL);