dim: make dim_calc_stats() inputs const pointers

dim: make dim_calc_stats() inputs const pointers

Make the start and end arguments to dim_calc_stats() const pointers
to clarify that the function does not modify their values.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Arthur Kiyanovski <akiyano@amazon.com>
Link: https://patch.msgid.link/20241031002326.3426181-1-csander@purestorage.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>