ACPI / extlog: Check for RDMSR failure

extlog_init() uses rdmsrl() to read an MSR, which on older CPUs
provokes a error message at boot:

unchecked MSR access error: RDMSR from 0x179 at rIP: 0xcd047307 (native_read_msr+0x7/0x40)

Use rdmsrl_safe() instead, and return -ENODEV if it fails.

Reported-by: [e-mail]
References: https://bugs.debian.org/971058
Cc: All applicable <[e-mail]>
Signed-off-by: Ben Hutchings <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/acpi_extlog.c

···
 	u64 cap;
 	int rc;
 
-	rdmsrl(MSR_IA32_MCG_CAP, cap);
-
-	if (!(cap & MCG_ELOG_P) || !extlog_get_l1addr())
+	if (rdmsrl_safe(MSR_IA32_MCG_CAP, &cap) ||
+	    !(cap & MCG_ELOG_P) ||
+	    !extlog_get_l1addr())
 		return -ENODEV;
 
 	rc = -EINVAL;