x86: mce: Add the dropped timer interval init back

commit 82f7af09 ("x86/mce: Cleanup timer mess) dropped the
initialization of the per cpu timer interval. Duh :(

Restore the previous behaviour.

Reported-by: Chen Gong <gong.chen@linux.intel.com>
Cc: bp@amd64.org
Cc: tony.luck@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>