x86: Do not try to disable hpet if it hasn't been initialized before

hpet_disable is called unconditionally on machine reboot if hpet support
is compiled in the kernel.
hpet_disable only checks if the machine is hpet capable but doesn't make
sure that hpet has been initialized.

[ tglx: Made it a one liner and removed the redundant hpet_address check ]
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: NVenkatesh Pallipadi <venki@google.com>
LKML-Reference: <alpine.DEB.2.00.1007211726240.22235@kaball-desktop>
Cc: stable@kernel.org
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/hpet.c

@@ -964,7 +964,7 @@ fs_initcall(hpet_late_init);
 
 void hpet_disable(void)
 {
-	if (is_hpet_capable()) {
+	if (is_hpet_capable() && hpet_virt_address) {
 		unsigned int cfg = hpet_readl(HPET_CFG);
 
 		if (hpet_legacy_int_enabled) {