btrfs: use cached state when falling back from NOCoW write to CoW write

We have a cached extent state record from the previous extent locking so
we can use when setting the EXTENT_NORESERVE in the range, allowing the
operation to be faster if the extent io tree is relatively large.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>