KVM: arm64: PMU: Fix PMCR_EL0 reset value

ARMV8_PMU_PMCR_N_MASK is an unshifted value which results in the wrong
reset value for PMCR_EL0, so shift it to fix it.

This fixes the following error when running qemu:

  $ qemu-system-aarch64 -cpu host -machine type=virt,accel=kvm -kernel ...

  target/arm/helper.c:1813: pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed.

Fixes: 292e8f14 ("KVM: arm64: PMU: Simplify PMCR_EL0 reset handling")
Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221209164446.1972014-2-james.clark@arm.com

arch/arm64/kvm/sys_regs.c

@@ -646,7 +646,7 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 		return;
 
 	/* Only preserve PMCR_EL0.N, and reset the rest to 0 */
-	pmcr = read_sysreg(pmcr_el0) & ARMV8_PMU_PMCR_N_MASK;
+	pmcr = read_sysreg(pmcr_el0) & (ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
 	if (!kvm_supports_32bit_el0())
 		pmcr |= ARMV8_PMU_PMCR_LC;