PM / devfreq: Add MODULE_LICENSE for arm-memlat-mon

Fix the following warning from modpost:

   WARNING: modpost: missing MODULE_LICENSE() in drivers/devfreq/arm-memlat-mon.o

Fixes: a4e0d26f ("PM / devfreq: Introduce a memory-latency governor")
Change-Id: Ic0dedbad2d3462ee407e5f2d5bcb9ded6e6ac83f
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>