libc: io: fix ringbuf_read/write not returning the correct values

lib/libc/io/stdio/ringbuf.c

@@ -145,7 +145,7 @@ long __libc_ringbuf_read(struct ringbuf *buf, void *p, size_t count)
 
 		memcpy(dest, src, to_copy);
 
-		nr_read += available;
+		nr_read += to_copy;
 		__libc_ringbuf_put_read_buffer(buf, &src, &to_copy);
 	}
 
@@ -183,7 +183,7 @@ long __libc_ringbuf_write(struct ringbuf *buf, const void *p, size_t count)
 
 		memcpy(dest, src, to_copy);
 
-		nr_written += available;
+		nr_written += to_copy;
 		__libc_ringbuf_put_write_buffer(buf, &dest, &to_copy);
 	}