RISC-V: KVM: Fix the initial sample period value

RISC-V: KVM: Fix the initial sample period value

The initial sample period value when counter value is not assigned
should be set to maximum value supported by the counter width.
Otherwise, it may result in spurious interrupts.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20240420151741.962500-11-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>