btrfs: remove redundant extent_buffer_uptodate() checks after read_tree_block()

btrfs: remove redundant extent_buffer_uptodate() checks after read_tree_block()

We have several places that call extent_buffer_uptodate() after reading a
tree block with read_tree_block(), but that is redundant since we already
call extent_buffer_uptodate() in the call chain of read_tree_block():

  read_tree_block()
     btrfs_read_extent_buffer()
        read_extent_buffer_pages()
           returns -EIO if extent_buffer_uptodate() returns false

So remove those redundant checks.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>