x86/mce: Remove redundant check from mce_device_create()

mce_device_create() is called only from mce_cpu_online() which in turn
will be called iff MCA support is available. That is, at the time of
mce_device_create() call it's guaranteed that MCA support is available.
No need to duplicate this check so remove it.

  [ bp: Massage commit message. ]

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231107165529.407349-1-nik.borisov@suse.com