KVM: x86: Optimize local variable in start_sw_tscdeadline()

Change the data type of the local variable this_tsc_khz to u32 because
virtual_tsc_khz is also declared as u32.

Since do_div() casts the divisor to u32 anyway, changing the data type
of this_tsc_khz to u32 also removes the following Coccinelle/coccicheck
warning reported by do_div.cocci:

  WARNING: do_div() does a 64-by-32 division, please consider using div64_ul instead
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Link: https://lore.kernel.org/r/20240814203345.2234-2-thorsten.blum@toblux.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/lapic.c

@@ -1944,7 +1944,7 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
 	u64 ns = 0;
 	ktime_t expire;
 	struct kvm_vcpu *vcpu = apic->vcpu;
-	unsigned long this_tsc_khz = vcpu->arch.virtual_tsc_khz;
+	u32 this_tsc_khz = vcpu->arch.virtual_tsc_khz;
 	unsigned long flags;
 	ktime_t now;