opengl: correct detection of virtual packages having no dependencies

I believe the original intent was to make it that the configure step
for the opengl virtual packages fails if there is not at least one
dependency. This patch fixes the logic so that it actually fails if
dependency list is empty

Signed-off-by: Will Wagner <will_wagner@carallon.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/opengl/libegl/libegl.mk

@@ -10,7 +10,7 @@ ifeq ($(BR2_PACKAGE_RPI_USERLAND),y)
 LIBEGL_DEPENDENCIES += rpi-userland
 endif
 
-ifeq ($(LIBEGL_DEPENDENCIES),y)
+ifeq ($(LIBEGL_DEPENDENCIES),)
 define LIBEGL_CONFIGURE_CMDS
 	echo "No libEGL implementation selected. Configuration error."
 	exit 1

package/opengl/libgles/libgles.mk

@@ -10,7 +10,7 @@ ifeq ($(BR2_PACKAGE_RPI_USERLAND),y)
 LIBGLES_DEPENDENCIES += rpi-userland
 endif
 
-ifeq ($(LIBGLES_DEPENDENCIES),y)
+ifeq ($(LIBGLES_DEPENDENCIES),)
 define LIBGLES_CONFIGURE_CMDS
 	echo "No libGLES implementation selected. Configuration error."
 	exit 1

package/opengl/libopenvg/libopenvg.mk

@@ -10,7 +10,7 @@ ifeq ($(BR2_PACKAGE_RPI_USERLAND),y)
 LIBOPENVG_DEPENDENCIES += rpi-userland
 endif
 
-ifeq ($(LIBOPENVG_DEPENDENCIES),y)
+ifeq ($(LIBOPENVG_DEPENDENCIES),)
 define LIBOPENVG_CONFIGURE_CMDS
 	echo "No libOpenVG implementation selected. Configuration error."
 	exit 1