netfs: Fix netfs_page_mkwrite() to flush conflicting data, not wait

Fix netfs_page_mkwrite() to use filemap_fdatawrite_range(), not
filemap_fdatawait_range() to flush conflicting data.

Fixes: 102a7e2c

 ("netfs: Allow buffered shared-writeable mmap through netfs_page_mkwrite()")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/614300.1719228243@warthog.procyon.org.uk


cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>