iwlwifi: fix various spelling and typos

Fixing various spelling errors and typos. Mostly in comments. In total
27 words were corrected, some of which occurred more than ones.

Signed-Of-By: Ian Schram <ischram@telenet.be>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>