Initialize pvalue attribute name.

def _init_pval_name(**kws):
        """Initialize pvalue attribute name."""
        if 'pval_name' in kws:
            return kws['pval_name']
        if 'goea_results' in kws:
            goea = kws['goea_results']
            if goea:
                return "p_{M}".format(M=goea[0].method_flds[0].fieldname)