kconfig: return 'false' instead of 'no' in bool function

menu_is_visible() is a bool function and should use boolean return
values. "no" is a tristate value which happens to also have a value
of 0, but we should nevertheless use the right symbol for it.

This is a very minor cleanup with no semantic change.

Fixes: 86e187ff ("kconfig: add an option to determine a menu's visibility")
Cc: Arnaud Lacombe <lacombar@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Michal Marek <mmarek@suse.com>