zprop: fix value help for ZPOOL_PROP_CAPACITY

It's a percentage and documented as such, but we were showing it as
<size>.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes openzfs#16881

Author: robn

module/zcommon/zpool_prop.c

@@ -105,7 +105,7 @@ zpool_prop_init(void)
 	    PROP_READONLY, ZFS_TYPE_POOL, "<percent>", "FRAG", B_FALSE,
 	    sfeatures);
 	zprop_register_number(ZPOOL_PROP_CAPACITY, "capacity", 0, PROP_READONLY,
-	    ZFS_TYPE_POOL, "<size>", "CAP", B_FALSE, sfeatures);
+	    ZFS_TYPE_POOL, "<percent>", "CAP", B_FALSE, sfeatures);
 	zprop_register_number(ZPOOL_PROP_GUID, "guid", 0, PROP_READONLY,
 	    ZFS_TYPE_POOL, "<guid>", "GUID", B_TRUE, sfeatures);
 	zprop_register_number(ZPOOL_PROP_LOAD_GUID, "load_guid", 0,