xen: make HYPERVISOR_set_debugreg() always_inline

HYPERVISOR_set_debugreg() is being called from noinstr code, so it
should be attributed "always_inline".

Fixes: 7361fac0 ("x86/xen: Make set_debugreg() noinstr")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20211125092056.24758-3-jgross@suse.comSigned-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/include/asm/xen/hypercall.h

@@ -281,7 +281,7 @@ HYPERVISOR_callback_op(int cmd, void *arg)
 	return _hypercall2(int, callback_op, cmd, arg);
 }
 
-static inline int
+static __always_inline int
 HYPERVISOR_set_debugreg(int reg, unsigned long value)
 {
 	return _hypercall2(int, set_debugreg, reg, value);