fs/9p/vfs_file.c: use new return type vm_fault_t

Use new return type vm_fault_t for page_mkwrite handler.

See 1c8f4220 ("mm: change return type to vm_fault_t") for reference.

Link: http://lkml.kernel.org/r/20180702154928.GA3964@jordon-HP-15-Notebook-PCSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Jun Piao <piaojun@huawei.com>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

fs/9p/vfs_file.c

@@ -533,7 +533,7 @@ v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
 	return retval;
 }
 
-static int
+static vm_fault_t
 v9fs_vm_page_mkwrite(struct vm_fault *vmf)
 {
 	struct v9fs_inode *v9inode;