x86/apm: Fix spelling mistake: "caculate" -> "calculate"

Trivial fix to spelling mistake in module parameter description text

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: kernel-janitors@vger.kernel.org
Cc: "H . Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180428092448.6493-1-colin.king@canonical.com