Btrfs: cleanup 'start' subtraction from try uncompressed inline extent

Was added in:
  c8b97818
  "Btrfs: Add zlib compression support"
Survive to near time (from 08.10.2008).

Because 'start' checked for zero before branch, so it's safe to remove
that subtraction.
Signed-off-by: NTimofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: NSatoru Takeuchi <satoru.takeuchi@gmail.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -570,7 +570,7 @@ static noinline void compress_file_range(struct inode *inode,
 cont:
 	if (start == 0) {
 		/* lets try to make an inline extent */
-		if (ret || total_in < (actual_end - start)) {
+		if (ret || total_in < actual_end) {
 			/* we didn't compress the entire range, try
 			 * to make an uncompressed inline extent.
 			 */