In is_valid_bugaddr(), probe_kernel_address() is called with
the PC casted to (bug_inst_t __user *) but this function
only take a plain void* as argument, not a __user pointer.

Fix this by removing the unnneded __user in the cast.
Signed-off-by: NLuc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>