[f2fs] code refactoring:
change unsigned int style to uint32_t (f2fs_internal.h)

  (comment: #142 https://fuchsia-review.googlesource.com/c/third_party/f2fs/+/511840)

Change-Id: Ie0fbc9bdd3584e1fe1d2fbcf8bfacbb8a753f5db
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/f2fs/+/531071
Reviewed-by: Brett Wilson <brettw@google.com>
diff --git a/f2fs_internal.h b/f2fs_internal.h
index c504c36..c7065ef 100644
--- a/f2fs_internal.h
+++ b/f2fs_internal.h
@@ -144,7 +144,7 @@
   /* NAT cache management */
   RadixTreeRoot nat_root; /* root of the nat entry cache */
   rwlock_t nat_tree_lock;          /* protect nat_tree_lock */
-  uint64_t nat_cnt = 0;            /* the # of cached nat entries */
+  uint32_t nat_cnt = 0;            /* the # of cached nat entries */
   list_node_t nat_entries;         /* cached nat entry list (clean) */
   list_node_t dirty_nat_entries;   /* cached nat entry list (dirty) */