confile_utils: cleanup strprint()

src/lxc/confile_utils.h

@@ -15,10 +15,8 @@
 			len = snprintf(str, inlen, ##__VA_ARGS__);                    \
 		else                                                                  \
 			len = snprintf((char *){""}, 0, ##__VA_ARGS__);               \
-		if (len < 0) {                                          \
-			SYSERROR("failed to create string");            \
-			return -1;                                      \
-		};                                                      \
+		if (len < 0)                                                          \
+			return log_error_errno(-EIO, EIO, "failed to create string"); \
 		fulllen += len;                                                       \
 		if (inlen > 0) {                                                      \
 			if (str)                                                      \