fellow_cache: Flexelint polish

avoid comparison between signed and unsigned.

We know that (have) is positive here because of the explicit test for
< 0 two lines above, so it is save to cast to the type of the rhd
operand.

Ref a9700c63
Ref #65

src/fellow_cache.c

@@ -791,7 +791,7 @@ struct fellow_cache_obj {
 #define FCR_IOFAILHOW(str, have, want)					\
 	((have) < 0 ? errno = (int)(-(have)), FCR_IOFAIL(str " error")	\
 	: ((have) == 0 ? FCR_IOFAIL(str " zero")			\
-	: ((have) < (want) ? FCR_IOFAIL(str " short")			\
+	: ((typeof(want))(have) < (want) ? FCR_IOFAIL(str " short")	\
 	: FCR_IOFAIL(str " other"))))
 
 const char * const fellow_cache_res_s[FCR_LIM] = {