If you look at the data sheet you will see there is no register called TC_CV, there is however a TC_CV0, TC_CV1 and TC_CV2.
It also tells you the address, each register occupies four bytes:-
37.7.13 Name:
Address: Access:
TC Counter Value Register
TC_CVx [x=0..2]
0x40080010 (0)[0], 0x40080050 (0)[1], 0x40080090 (0)[2], 0x40084010 (1)[0], 0x40084050 (1)[1], 0x40084090 (1)[2], 0x40088010 (2)[0], 0x40088050 (2)[1], 0x40088090 (2)[2]
Read-only • CV: Counter Value
CV contains the counter value in real time.