toolchain: fix 3.16 selection for custom version

Fix d'oh typo from 911516f1b6dec4b2985a1f454949f8d9d10f6ef5 that
prevents custom version string 3.16 headers from working properly.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-headers/Config.in.host

@@ -82,7 +82,7 @@ choice
 
 config BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_16
 	bool "3.16.x"
-	select BR2_PACKAGE_HEADERS_AT_LEAST_3_16
+	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_16
 
 config BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_15
 	bool "3.15.x"