openntpd: fix Config.in comment dependency

BR2_PACKAGE_OPENNTPD has a "depends on !BR2_PACKAGE_NTP" because the
openntpd package conflicts with the ntp package.

So the Config.in comment of openntpd should also not be visible when ntp
is selected. Otherwise the comment will show up when the user has a
non-NPTL toolchain, and once he enables NPTL support, the comment
disappears, but the package option doesn't appear.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/openntpd/Config.in

@@ -13,4 +13,5 @@ config BR2_PACKAGE_OPENNTPD
 
 comment "openntpd needs a toolchain w/ NPTL"
 	depends on BR2_USE_MMU
+	depends on !BR2_PACKAGE_NTP
 	depends on !BR2_TOOLCHAIN_HAS_THREADS_NPTL