iwlwifi: fix ACPI table revision checks

We can't check for the ACPI table revision validity in the same if
where we check if the package was read correctly, because we return
PTR_ERR(pkg) and if the table is not valid but the pointer is, we
would return a valid pointer as an error.  Fix that by moving the
table checks to a separate if and return -EINVAL if it's not valid.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>