ocfs2: fix write() performance regression

ocfs2: fix write() performance regression

ocfs2: fix write() performance regression

patch 4e9563fd55ff4479f2b118d0757d121dd0cfc39c in mainline.

On file systems which don't support sparse files, Ocfs2_map_page_blocks()
was reading blocks on appending writes. This caused write performance to
suffer dramatically. Fix this by detecting an appending write on a nonsparse
fs and skipping the read.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>