x86/mem_sharing: fix wrong field name used in 2c5119d

The arch_domain struct has "msr", not "msrs".

Spotted by a TravisCI Randconfig build.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/mm/mem_sharing.c

@@ -1781,7 +1781,7 @@ static int fork(struct domain *cd, struct domain *d)
         domain_pause(d);
         cd->max_pages = d->max_pages;
         *cd->arch.cpuid = *d->arch.cpuid;
-        *cd->arch.msrs = *d->arch.msrs;
+        *cd->arch.msr = *d->arch.msr;
         cd->parent = d;
     }