Correct compilation errors reported by GCC 10/11

New `zfs_type_t` value `ZFS_TYPE_INVALID` is introduced.
Variable initialization is now possible to make GCC happy.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #12167
Closes #13103

include/sys/fs/zfs.h

@@ -50,6 +50,7 @@ extern "C" {
  * combined into masks that can be passed to various functions.
  */
 typedef enum {
+	ZFS_TYPE_INVALID	= 0,
 	ZFS_TYPE_FILESYSTEM	= (1 << 0),
 	ZFS_TYPE_SNAPSHOT	= (1 << 1),
 	ZFS_TYPE_VOLUME		= (1 << 2),