x86: let early_reserve_e820 update e820_saved too

so when it is called after early_param, e820_saved get updated too.
esp for mpc update.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>