btrfs: Fix the wrong condition judgment about subset extent map

btrfs: Fix the wrong condition judgment about subset extent map

commit 32be3a1ac6d09576c57063c6c350ca36eaebdbd3 upstream.

Previous commit: btrfs: Fix and enhance merge_extent_mapping() to insert
best fitted extent map
is using wrong condition to judgement whether the range is a subset of a
existing extent map.

This may cause bug in btrfs no-holes mode.

This patch will correct the judgment and fix the bug.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>