hid: fix misassignment

The code does not have any effect as is, fix it.

Spotted by clang analyzer:
/src/qemu/hw/hid.c:99:13: warning: Value stored to 'x1' is never read
            x1 = 1;

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/hid.c b/hw/hid.c
index ec066cf..03761ab 100644
--- a/hw/hid.c
+++ b/hw/hid.c
@@ -96,7 +96,7 @@
         /* Windows drivers do not like the 0/0 position and ignore such
          * events. */
         if (!(x1 | y1)) {
-            x1 = 1;
+            e->xdx = 1;
         }
     }
     e->dz += z1;