ACPI EC: Fix regression due to use of uninitialized variable

breakage introduced by following patch
commit 27663c58


Author: Matthew Wilcox <willy@linux.intel.com>
Date:   Fri Oct 10 02:22:59 2008 -0400

acpi_evaluate_integer() does not clear passed variable if
there is an error at evaluation.
So if we ignore error, we must supply initialized variable.

http://bugzilla.kernel.org/show_bug.cgi?id=11917

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Tested-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>