wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/scrub.c

@@ -4279,7 +4279,7 @@ static int copy_nocow_pages_for_inode(u64 inum, u64 offset, u64 root,
 		return PTR_ERR(inode);
 
 	/* Avoid truncate/dio/punch hole.. */
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	inode_dio_wait(inode);
 
 	physical_for_dev_replace = nocow_ctx->physical_for_dev_replace;
@@ -4358,7 +4358,7 @@ next_page:
 	}
 	ret = COPY_COMPLETE;
 out:
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	iput(inode);
 	return ret;
 }