samples: net: irc_bot: fix null pointer deref

samples/net/irc_bot/src/irc-bot.c:368:36:
warning: 'c' may be used uninitialized in this function
[-Wmaybe-uninitialized]
  for (cc = &chan->irc->chans, c = c->irc->chans;
                                   ^
As suggested by Leandro Pereira <leandro.pereira@intel.com>
adjusted to:
  for (cc = &chan->irc->chans, c = chan->irc->chans;

Change-Id: Icd490059e0b97f95408dd7bad3f1783a215c5edb
Signed-off-by: Michael Scott <michael.scott@linaro.org>