powercap/RAPL: prevent overridding bits outside of the mask

Fixes wrong bits shift operation in the rapl_write_data_raw function, which
might cause overridding bits outside of the mask.

For example, writing new TIME_WINDOW1 value can override POWER_LIMIT1.

Signed-off-by: Adam Lessnau <adam.lessnau@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>