ibmpc: Fix AT 'request to send' signaling

Without this fix Realforce 101 PS/2 fails to receive 'set indicator'
command sometimes when pressing Caps Lock and some keys simultaneously.

before fix:
      ____     ______
clock     \___/
      ________
data          \_______
          | 100|

after fix:
      ____          __
clock     \________/
      ________
data          \_______
          | 100| 100|

tmk_core/protocol/ibmpc.c

@@ -109,6 +109,7 @@ int16_t ibmpc_host_send(uint8_t data)
 
     /* 'Request to Send' and Start bit */
     data_lo();
+    wait_us(100);
     clock_hi();
     WAIT(clock_lo, 10000, 1);   // 10ms [5]p.50