cpufreq: Protected access of policy attribute

It takes read RW semaphore to access policy governor

bug 997731

Change-Id: Ibdc3dd54cf6076c0fef4bc58f144e4bcb4631d76
Signed-off-by: Puneet Saxena <puneets@nvidia.com>
Reviewed-on: http://git-master/r/107079
GVS: Gerrit_Virtual_Submit
Reviewed-by: Sang-Hun Lee <sanlee@nvidia.com>
Reviewed-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>