linux-user: fix comment s/atomic_write/atomic_set/

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <20180811211011.6277-1-cota@braap.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/qemu.h

@@ -143,7 +143,7 @@ typedef struct TaskState {
     /* Nonzero if process_pending_signals() needs to do something (either
      * handle a pending signal or unblock signals).
      * This flag is written from a signal handler so should be accessed via
-     * the atomic_read() and atomic_write() functions. (It is not accessed
+     * the atomic_read() and atomic_set() functions. (It is not accessed
      * from multiple threads.)
      */
     int signal_pending;