dosfstools: place files in /sbin, not in /usr/sbin

dosfstools: place files in /sbin, not in /usr/sbin

systemd expects fsck programs to be located in /sbin and fails for
dosfstools with

| Checking was requested for ..., but /sbin/fsck.vfat cannot be used: No such file or directory

Other fsck programs (e.g. ext4) are located in /sbin already so move
vfat programs into this directory too.

(From OE-Core rev: fa579cb243b8441d95e6c129e07d9e141f808539)

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>