drm/i915/alpm: Remove error handling from get_lfps_cycle_min_max_time

drm/i915/alpm: Remove error handling from get_lfps_cycle_min_max_time

Getter for LFPS cycle min/max times is unnecessarily checking faulty port
clock value. This doesn't make sense as erroneous port clock value would
have been noticed already at this point. Remove this check and use 140/800
ns always when port clock > 540000.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://lore.kernel.org/r/20250912064035.335329-1-jouni.hogander@intel.com