Fix bug in parsing of cli option --tx-size-search-method

--tx-size-search-method needs argument. Hence CLI parsing of this option is
modified to accept arguments.

Change-Id: I09318a7ec025c139029d40d99bf52bff521f81a6
diff --git a/apps/aomenc.c b/apps/aomenc.c
index 7b01af2..bd767c6 100644
--- a/apps/aomenc.c
+++ b/apps/aomenc.c
@@ -478,7 +478,7 @@
     ARG_DEF(NULL, "enable-tx64", 1,
             "Enable 64-pt transform (0: false, 1: true (default))");
 static const arg_def_t tx_size_search_method =
-    ARG_DEF(NULL, "tx-size-search-method", 0,
+    ARG_DEF(NULL, "tx-size-search-method", 1,
             "Set transform block size search method "
             "(0: Full RD (default), 1: Fast RD, 2: use largest allowed)");
 static const arg_def_t enable_flip_idtx =