drbd-utils: fix typo in variable name

As pointed out during the check-package discussion, there is a typo in a
variable name:

http://lists.busybox.net/pipermail/buildroot/2016-December/180765.html

Reported-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/drbd-utils/drbd-utils.mk

@@ -14,14 +14,14 @@ DRBD_UTILS_CONF_OPTS = --with-distro=generic --without-manual
 
 ifeq ($(BR2_INIT_SYSTEMD),y)
 DRBD_UTILS_CONF_OPTS += --with-initscripttype=systemd
-DRDB_UTILS_DEPENDENCIES += systemd
+DRBD_UTILS_DEPENDENCIES += systemd
 else
 DRBD_UTILS_CONF_OPTS += --with-initscripttype=sysv
 endif
 
 ifeq ($(BR2_PACKAGE_HAS_UDEV),y)
 DRBD_UTILS_CONF_OPTS += --with-udev=yes
-DRDB_UTILS_DEPENDENCIES += udev
+DRBD_UTILS_DEPENDENCIES += udev
 else
 DRBD_UTILS_CONF_OPTS += --with-udev=no
 endif