UPSTREAM: gfs2: Add wrapper for iomap_file_buffered_write

commit 2eb7509a upstream

Add a wrapper around iomap_file_buffered_write.  We'll add code for when
the operation needs to be retried here later.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit b88b9985)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I144fa4b02e35bb8a1c9ac1f1f0ed149c5cdf91b6