stagefright amrwbenc: Remove a useless check

Since the Length field is unsigned, the comparison will always
be false. The corresponding code in the aac encoder doesn't have
any check for Length.

This avoids a warning about comparison always being false.

Change-Id: I57c28ff9d09cb9ac4effeaeb40db608ab976acc6
diff --git a/media/libstagefright/codecs/amrwbenc/src/voAMRWBEnc.c b/media/libstagefright/codecs/amrwbenc/src/voAMRWBEnc.c
index 0f4d689..ea9da52 100644
--- a/media/libstagefright/codecs/amrwbenc/src/voAMRWBEnc.c
+++ b/media/libstagefright/codecs/amrwbenc/src/voAMRWBEnc.c
@@ -1702,7 +1702,7 @@
 	gData = (Coder_State *)hCodec;
 	stream = gData->stream;
 
-	if(NULL == pInput || NULL == pInput->Buffer || 0 > pInput->Length)
+	if(NULL == pInput || NULL == pInput->Buffer)
 	{
 		return VO_ERR_INVALID_ARG;
 	}