MIPS: Clean up notify_die() usage.

MIPS: Clean up notify_die() usage.

The sixth argument of notify_die() is a signal number, the fifth is a
trap number.

Instead of passing a signal number in a randomly selected argument,
pass it in the sixth.  Extract the exception code from regs and pass
that as the trap number.

Get rid of redundant cast, and remove some gratuitous spaces.

Nobody actually does anything with the signal number or trap number,
but we might as well populate them with sensible values.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1532/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>