Fix build - only include exynos files if present

Change-Id: I6c56185442bcd9bea7c8699bfeb4adbeb97d0f1e
diff --git a/device.mk b/device.mk
index 3e3ebbd..2c44340 100644
--- a/device.mk
+++ b/device.mk
@@ -184,7 +184,7 @@
     charger \
     charger_res_images
 
-$(call inherit-product, hardware/samsung_slsi/exynos5/exynos5.mk)
+$(call inherit-product-if-exists, hardware/samsung_slsi/exynos5/exynos5.mk)
 $(call inherit-product-if-exists, vendor/samsung_slsi/exynos5/exynos5-vendor.mk)
 $(call inherit-product-if-exists, vendor/samsung/manta/device-vendor.mk)