fellow_cache: Flexelint polish

explicit cast for errno assignment

Ref a9700c63
Ref #65

src/fellow_cache.c

@@ -789,7 +789,7 @@ struct fellow_cache_obj {
 #define FCR_ALLOCFAIL(str) FCR_ALLOCERR(FC_ERRSTR(str))
 #define FCR_IOFAIL(str) FCR_IOERR(FC_ERRSTR(str))
 #define FCR_IOFAILHOW(str, have, want)					\
-	((have) < 0 ? errno = -(have), FCR_IOFAIL(str " error")		\
+	((have) < 0 ? errno = (int)(-(have)), FCR_IOFAIL(str " error")	\
 	: ((have) == 0 ? FCR_IOFAIL(str " zero")			\
 	: ((have) < (want) ? FCR_IOFAIL(str " short")			\
 	: FCR_IOFAIL(str " other"))))