qt: fix qconfig configure parameter

The Qt configure option for specifying a custom qconfig.h
file changed from -config to -qconfig. This makes the
corresponding change in qt.mk.

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/qt/qt.mk

@@ -24,7 +24,7 @@ endif
 QT_CONFIG_FILE=$(call qstrip,$(BR2_PACKAGE_QT_CONFIG_FILE))
 
 ifneq ($(QT_CONFIG_FILE),)
-QT_CONFIGURE_OPTS += -config buildroot
+QT_CONFIGURE_OPTS += -qconfig buildroot
 endif
 
 QT_CFLAGS = $(TARGET_CFLAGS)