PM / devfreq: bw_hwmon: Reflow some code

Fix up style in this driver probe routine to use newer mechanisms
like of_device_get_match_data() and to not use things like
addresses of functions to assign function pointers. This makes
the code more readable.

Change-Id: Ib07edc0051fe9319e9a40cda7ba79646ce59b7e4
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>