docbook: fix signal_pending() argument

Since signal_pending() takes a task_struct pointer as an argument, update
the example to pass in 'current'.

Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/DocBook/kernel-hacking.tmpl

@@ -352,7 +352,7 @@ asmlinkage long sys_mycall(int arg)
   </para>
 
   <programlisting>
-if (signal_pending()) 
+if (signal_pending(current))
         return -ERESTARTSYS;
   </programlisting>