mtools: upgrade 4.0.42 -> 4.0.43

mtools: upgrade 4.0.42 -> 4.0.43

Changelog:
==========
- Fix root directory test in mattrib
- -b BiosDisk flag for mformat to allow setting physdrive to
  a user-specified value
- Clearer error message in mformat when trying to mformat a
  disk whose total size is not known
- Make recursive copy more consistent
- Trailing slash now always implies target should be a directory
- Code cleanup

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>