x86/idt: Remove address operator on function machine_check()

machine_check is function address, the address operator on it is nop for
compiler.

Make it consistent with the other function addresses in the same file.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200419144049.1906-3-laijs@linux.alibaba.com