opp_find_freq_ceil and opp_get_voltage are documented as requiring
rcu_lock to be held.  So hold it.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Kevin Hilman <khilman@ti.com>
        freq = clk->rate;
        clk_put(clk);
 
+       rcu_read_lock();
        opp = opp_find_freq_ceil(dev, &freq);
        if (IS_ERR(opp)) {
+               rcu_read_unlock();
                pr_err("%s: unable to find boot up OPP for vdd_%s\n",
                        __func__, vdd_name);
                goto exit;
        }
 
        bootup_volt = opp_get_voltage(opp);
+       rcu_read_unlock();
        if (!bootup_volt) {
                pr_err("%s: unable to find voltage corresponding "
                        "to the bootup OPP for vdd_%s\n", __func__, vdd_name);