direct_IO: use iov_iter_rw() instead of rw everywhere

The rw parameter to direct_IO is redundant with iov_iter->type, and
treated slightly differently just about everywhere it's used: some users
do rw & WRITE, and others do rw == WRITE where they should be doing a
bitwise check. Simplify this with the new iov_iter_rw() helper, which
always returns either READ or WRITE.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index c3929fb..e8482b8 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -267,7 +267,7 @@
 #else
 	VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);
 
-	if (rw == READ)
+	if (iov_iter_rw(iter) == READ)
 		return nfs_file_direct_read(iocb, iter, pos);
 	return nfs_file_direct_write(iocb, iter, pos);
 #endif /* CONFIG_NFS_SWAP */