android: use := operator for assigning MESA_VERSION

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/Android.common.mk b/Android.common.mk
index 3e6d4c3..e34f206 100644
--- a/Android.common.mk
+++ b/Android.common.mk
@@ -33,7 +33,7 @@
 LOCAL_C_INCLUDES += \
 	$(MESA_TOP)/include
 
-MESA_VERSION=$(shell cat $(MESA_TOP)/VERSION)
+MESA_VERSION := $(shell cat $(MESA_TOP)/VERSION)
 # define ANDROID_VERSION (e.g., 4.0.x => 0x0400)
 LOCAL_CFLAGS += \
 	-DPACKAGE_VERSION=\"$(MESA_VERSION)\" \