x86, msr: Have the _safe MSR functions return -EIO, not -EFAULT

For some reason, the _safe MSR functions returned -EFAULT, not -EIO.
However, the only user which cares about the return code as anything
other than a boolean is the MSR driver, which wants -EIO.  Change it
to -EIO across the board.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

arch/x86/xen/enlighten.c

@@ -713,7 +713,7 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 	set:
 		base = ((u64)high << 32) | low;
 		if (HYPERVISOR_set_segment_base(which, base) != 0)
-			ret = -EFAULT;
+			ret = -EIO;
 		break;
 #endif