x86/entry/64: Simplify idtentry_body

All C functions which do not have an error code have been converted to the
new IDTENTRY interface which does not expect an error code in the
arguments. Spare the XORL.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202118.145811853@linutronix.de