btrfs: make wait_extent_bit() static

The function wait_extent_bit() is not used outside extent-io-tree.c so
make it static. Furthermore the function doesn't have the 'btrfs_' prefix.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-io-tree.c

@@ -767,8 +767,8 @@ static void wait_on_state(struct extent_io_tree *tree,
  * The range [start, end] is inclusive.
  * The tree lock is taken by this function
  */
-void wait_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, u32 bits,
-		     struct extent_state **cached_state)
+static void wait_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+			    u32 bits, struct extent_state **cached_state)
 {
 	struct extent_state *state;
 

fs/btrfs/extent-io-tree.h

@@ -193,7 +193,5 @@ int find_contiguous_extent_bit(struct extent_io_tree *tree, u64 start,
 bool btrfs_find_delalloc_range(struct extent_io_tree *tree, u64 *start,
 			       u64 *end, u64 max_bytes,
 			       struct extent_state **cached_state);
-void wait_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, u32 bits,
-		     struct extent_state **cached_state);
 
 #endif /* BTRFS_EXTENT_IO_TREE_H */