util-linux: fix chfn/chsh missing dependencies

chfn/chsh utilities need linux-pam.

Fixes:
  http://autobuild.buildroot.org/results/cfc/cfc5fd00b9db21b60efe8b74e9966b6192b1da17/



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>