fix build

Change-Id: I44a75f5451af053778be299b23274ecce9b2db76
diff --git a/applypatch/applypatch.h b/applypatch/applypatch.h
index e8ac3cc..fb58843 100644
--- a/applypatch/applypatch.h
+++ b/applypatch/applypatch.h
@@ -64,7 +64,7 @@
                      int retouch_flag);
 int SaveFileContents(const char* filename, const FileContents* file);
 void FreeFileContents(FileContents* file);
-int FindMatchingPatch(uint8_t* sha1, char** const patch_sha1_str,
+int FindMatchingPatch(uint8_t* sha1, const char** patch_sha1_str,
                       int num_patches);
 
 // bsdiff.c