doc/openocd: Fix buspirate example

Change-Id: Idcbe73220d7630953cb49e643a58a7ab05c395fa
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: http://openocd.zylin.com/6406
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

doc/openocd.texi

@@ -3349,7 +3349,7 @@ buspirate port /dev/ttyUSB0
 @deffn {Config Command} {buspirate speed} (normal|fast)
 Set the communication speed to 115k (normal) or 1M (fast). For example:
 @example
-buspirate mode normal
+buspirate speed normal
 @end example
 @end deffn