PM: intel_powerclamp: off by one in start_power_clamp()

This value has already been clamped correctly to 0 through 49 in
powerclamp_set_cur_state() so this patch doesn't actually change
anything.  But we should fix it anyway for consistency.

set_target_ratio is used as an offset into an array with
MAX_TARGET_RATIO (50) elements.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>