fellow_cache: rename fellow_cache_res field in fco

src/fellow_cache.c

@@ -717,7 +717,7 @@ struct fellow_cache_obj {
 	// ^^^ protected by mtx - do not add <64bit values
 
 	struct fellow_cache_lru		*lru;
-	struct fellow_cache_res		res;
+	struct fellow_cache_res		fcr;
 	uint8_t				ntouched;
 
 	struct buddy_ptr_extent		fco_mem;
@@ -790,12 +790,12 @@ struct fellow_cache_obj {
 #define FCR_IOFAIL(str) FCR_IOERR(FC_ERRSTR(str))
 
 static inline void
-fco_latch_err(struct fellow_cache_obj *fco, struct fellow_cache_res res)
+fco_latch_err(struct fellow_cache_obj *fco, struct fellow_cache_res fcr)
 {
-	assert(res.status != fcr_ok);
-	if (fco->res.status != fcr_ok)
+	assert(fcr.status != fcr_ok);
+	if (fco->fcr.status != fcr_ok)
 		return;
-	fco->res = res;
+	fco->fcr = fcr;
 }