drm/i915: Update rps interrupt limits

sysfs changes to rps min and max delay were only triggering an update
of the rps interrupt limits if the active delay required an update.
This change ensures that interrupt limits are always updated.

v2: correct compile issue missed on rebase
v3: add igt testcases to signed-off-by section

Testcase: igt/pm_rps/min-max-config-idle
Testcase: igt/pm_rps/min-max-config-loaded
Signed-off-by: Jeff McGee <jeff.mcgee@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>