Make get-file-size compatible with toybox stat

* Use the same format as mk_qemu_image.sh

Change-Id: I5df23f488006440075a00798a171f7a8856e097a
diff --git a/core/combo/HOST_linux-x86.mk b/core/combo/HOST_linux-x86.mk
index 4e83dc4..deed943 100644
--- a/core/combo/HOST_linux-x86.mk
+++ b/core/combo/HOST_linux-x86.mk
@@ -26,5 +26,5 @@
 
 # $(1): The file to check
 define get-file-size
-stat --format "%s" "$(1)" | tr -d '\n'
+stat -c "%s" "$(1)" | tr -d '\n'
 endef