Add protoype declaration for  b64_pton

Upstream-Status: Pending
Signed-off-by: Khem Raj <raj.khem@gmail.com>
--- a/adb/adb_auth_client.c
+++ b/adb/adb_auth_client.c
@@ -29,6 +29,7 @@
 
 #define TRACE_TAG TRACE_AUTH
 
+extern int b64_pton(const char* src, uint8_t* target, size_t targsize);
 
 struct adb_public_key {
     struct listnode node;