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_ioctl32.c b/fs/xfs/xfs_ioctl32.c
index 54e623b..dd4ba1d 100644
--- a/fs/xfs/xfs_ioctl32.c
+++ b/fs/xfs/xfs_ioctl32.c
@@ -454,7 +454,7 @@
 					&ops[i].am_length, 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(
@@ -464,7 +464,7 @@
 			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(