x86: properly gate clearing of PKU feature

setup_clear_cpu_cap() is __init and hence may not be called post-boot.
Note that opt_pku nevertheless is not getting __initdata added - see
e.g. commit 43fa95ae6a ("mm: make opt_bootscrub non-init").

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/cpu/common.c

@@ -463,7 +463,7 @@ void identify_cpu(struct cpuinfo_x86 *c)
 		this_cpu->c_init(c);
 
 
-   	if ( !opt_pku )
+   	if (c == &boot_cpu_data && !opt_pku)
 		setup_clear_cpu_cap(X86_FEATURE_PKU);
 
 	/*