pnpacpi: fix incorrect TEST_ALPHA() test

TEST_ALPHA() is broken and always returns 0.

[akpm@linux-foundation.org: return false for '@' as well, per Bjorn]
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>