The counter overflow CSR name is "scountovf" not "sscountovf".

Fix the csr name.

Fixes: 4905ec2f ("RISC-V: Add sscofpmf extension support")
Reviewed-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-2-atishp@rivosinc.comSigned-off-by: Anup Patel <anup@brainfault.org>