radv/rmv: Correct timestamp shifting
The shifting was off-by-one compared to how it is done in the kernel. Also, excess_length needs to be casted to uint64_t to prevent zeroing everything except the 5 LSBs. Fixes: abf3bcd6 ("radv: Add RMV resource tracking") Part-of: <mesa/mesa!20820> (cherry picked from commit e07729e8)