erofs: clean up erofs_map_blocks tracepoints

Since the new type of chunk-based files is introduced, there is no
need to leave flatmode tracepoints.

Rename to erofs_map_blocks instead.

Link: https://lore.kernel.org/r/20211209012918.30337-1-hsiangkao@linux.alibaba.com


Reviewed-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>