cfg80211: initialize reg_rule in __freq_reg_info()

cfg80211: initialize reg_rule in __freq_reg_info()

Sparse started warning on this function because we can potentially
return an uninitialized value.  The reason is that if the caller
passes a min_bw value that is higher then the last value in bws[], we
will not go into the loop and reg_rule will remain initialized.  This
cannot happen because the only caller of this function uses either 1
or 20 in min_bw, but the function will be more robust if we
pre-initialize the value.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210204154439.6c884ea7281c.I257278d03b0c1ae0aa6631672cfa48f1a95d5996@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>