cfg80211: add debug print when processing a channel

In the worst case you are seeing really odd things you want
more information than what is provided right now, for those
that insist and want debug info through CONFIG_CFG80211_REG_DEBUG
provide a print of when we are processing a channel and with what
regulatory rule.

Cc: Easwar Krishnan <easwar.krishnan@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>