man-db: Fix reproducibility issue

Executing a sequence like:

bitbake man-db
bitbake man-db -c clean
bitbake man-db -c package_write_deb -f

results in the ownership of files in the man-db package changing from "man/man"
to "6/12". This is due to base-passwd not being installed in the recipe
sysroot.

Add the missing dependency so even if a recipe "re-packages", the name
of the user/group is found and the packages are reproducible.

[YOCTO #14172]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>