Fix -Wformat error in crashdump.c

Cast statbuf.st_size to long before printing as %ld.

Bug: N/A
Test: watch TH for aosp-master/full-eng.
Change-Id: Icb25ccaeb9ca2e705039b87e4fae582a613605d0
diff --git a/microdroid/kdump/crashdump.c b/microdroid/kdump/crashdump.c
index a606d43..7f892f9 100644
--- a/microdroid/kdump/crashdump.c
+++ b/microdroid/kdump/crashdump.c
@@ -80,7 +80,7 @@
     if (fstat(vmcore, &statbuf) == -1) {
         FAIL("Failed to stat %s", DUMP_SOURCE);
     }
-    printf("Size is %ld bytes\n", statbuf.st_size);
+    printf("Size is %ld bytes\n", (long)statbuf.st_size);
 
     // sendfile(2) is faster, can't be used because /proc/vmcore doesn't support splice_read
     size_t dumped = 0;