signal/x86: Remove the pkey parameter from do_sigbus

The function do_sigbus never sets si_code to PKUERR so it can never
return a pkey to userspace.  Therefore remove the unusable pkey
parameter from do_sigbus.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>