switch a bunch of places to mnt_want_write_file()

it's both faster (in case when file has been opened for write) and cleaner.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index d99a905..b436e17 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -559,7 +559,7 @@
 					ops[i].am_flags);
 			break;
 		case ATTR_OP_SET:
-			ops[i].am_error = mnt_want_write(parfilp->f_path.mnt);
+			ops[i].am_error = mnt_want_write_file(parfilp);
 			if (ops[i].am_error)
 				break;
 			ops[i].am_error = xfs_attrmulti_attr_set(
@@ -569,7 +569,7 @@
 			mnt_drop_write(parfilp->f_path.mnt);
 			break;
 		case ATTR_OP_REMOVE:
-			ops[i].am_error = mnt_want_write(parfilp->f_path.mnt);
+			ops[i].am_error = mnt_want_write_file(parfilp);
 			if (ops[i].am_error)
 				break;
 			ops[i].am_error = xfs_attrmulti_attr_remove(