Kconfig: fix single letter command in scripts/config

The one letter commands in scripts/config didn't work and always
printed usage. Fix this here.

Cc: erick@openchill.org
Reported-by:  <erick@openchill.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>