iwlwifi: mvm: fix an out-of-bound access

commit ba3224db78034435e9ff0247277cce7c7bb1756c upstream.

The index for the elements of the ACPI object we dereference
was static. This means that if we called the function twice
we wouldn't start from 3 again, but rather from the latest
index we reached in the previous call.
This was dutifully reported by KASAN.

Fix this.

Cc: stable@vger.kernel.org
Fixes: 69964905 ("iwlwifi: mvm: add support for EWRD (Dynamic SAR) ACPI table")
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>