qseecom: Enable DFAB clock during bus scaling.

The driver returns a failure when calling to vote for DFAB clock.
- The clock was not enabled and set when bus scaling client
  registration was successfull.
- Added warning messages when bus scaling ioctl requests fail.
- Initializing uninitialized variables.

Change-Id: I076218fcccbb9144609311efde1eb4225d1729bf
Signed-off-by: Ramesh Masavarapu <rameshm@codeaurora.org>