ACPI: EC: fix compilation warning

Fix the warning introduced in commit c5279dee26c0e8d7c4200993bfc4b540d2469598,
and give the dummy variable a more verbose name.

  drivers/acpi/ec.c: In function 'acpi_ec_ecdt_probe':
  drivers/acpi/ec.c:1015: warning: ISO C90 forbids mixed declarations and code

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>