checkpatch: allow longer logging function names

The current $logFunction regular expression allows names like dev_warn,
e_dbg, netdev_info, etc, but some log functions are now written like
e_dev_warn, so allow 1 or 2 word blocks with an underscore before the
logging level.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>