inject.py: fix BPF verification fails due to register offset

run `./inject.py kmalloc -v '__x64_sys_mount()` gets the error:
"math between map_value pointer and register with unbounded min value is not allowed",
as the array len is 2:
    struct pid_struct {
        u64 curr_call; /* book keeping to handle recursion */
        u64 conds_met; /* stack pointer */
        u64 stack[2];
    };

but in `__x64_sys_mount_exit`

    /*
     * Generate exit logic
     */

    if (p->conds_met < 1 || p->conds_met >= 3)
            return 0;

    if (p->stack[p->conds_met - 1] == p->curr_call)
            p->conds_met--;

The check for the upper bound of the array is 3.

Signed-off-by: Wenbo Zhang <[email protected]>

tools/inject.py

@@ -178,7 +178,7 @@ def _get_exit_logic(self):
  if (p->stack[p->conds_met - 1] == p->curr_call)
  p->conds_met--;
  """
- return text % str(self.length + 1)
+ return text % str(self.length)
 
  def _generate_exit(self):
  prog = self._get_heading() + """