pw_kvs: Rename format.h to entry.h

Change-Id: Iad7148cad736d57a9ff5d23772a002c40508b6d4
diff --git a/pw_kvs/BUILD b/pw_kvs/BUILD
index 25a0eaa..bb38bcb 100644
--- a/pw_kvs/BUILD
+++ b/pw_kvs/BUILD
@@ -27,10 +27,10 @@
     srcs = [
         "alignment.cc",
         "checksum.cc",
+        "entry.cc",
         "flash_memory.cc",
-        "format.cc",
         "key_value_store.cc",
-        "pw_kvs_private/format.h",
+        "pw_kvs_private/entry.h",
         "pw_kvs_private/macros.h",
     ],
     hdrs = [