x86: use fixup_exception() in traps_64.c

Use the fixup_exception() helper instead of the open-coded
search_extable() users.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>