ext4: use truncate_pagecache() in collapse range

ext4: use truncate_pagecache() in collapse range

We should be using truncate_pagecache() instead of
truncate_pagecache_range() in the collapse range because we're
truncating page cache from offset to the end of file.
truncate_pagecache() also get rid of the private COWed pages from the
range because we're going to shift the end of the file.

Signed-off-by: Lukas Czerner <[email protected]>
Signed-off-by: "Theodore Ts'o" <[email protected]>