package/polkit: add linux-pam as a dependency if linux-pam is selected

Without linux-pam built first, polkit will throw a configuration error:
configure: error: Could not find pam/pam-devel, please install the needed packages.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/polkit/polkit.mk

@@ -24,6 +24,7 @@ POLKIT_CONF_OPTS = \
 	--disable-libsystemd-login
 
 ifeq ($(BR2_PACKAGE_LINUX_PAM),y)
+POLKIT_DEPENDENCIES += linux-pam
 POLKIT_CONF_OPTS += --with-authfw=pam
 else
 POLKIT_CONF_OPTS += --with-authfw=shadow