xen/x86: Constify the vCPU parameter for expand_xsave_states()

expand_xsave_states() is not meant to modify the vCPU. So the parameter
can be const.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

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

@@ -100,7 +100,7 @@ int __must_check validate_xstate(const struct domain *d,
                                  uint64_t xcr0, uint64_t xcr0_accum,
                                  const struct xsave_hdr *hdr);
 int __must_check handle_xsetbv(u32 index, u64 new_bv);
-void expand_xsave_states(struct vcpu *v, void *dest, unsigned int size);
+void expand_xsave_states(const struct vcpu *v, void *dest, unsigned int size);
 void compress_xsave_states(struct vcpu *v, const void *src, unsigned int size);
 
 /* extended state init and cleanup functions */

xen/arch/x86/xstate.c

@@ -172,7 +172,7 @@ static void setup_xstate_comp(uint16_t *comp_offsets,
  * It is the callers responsibility to ensure that there is xsave state to
  * serialise, and that the provided buffer is exactly the right size.
  */
-void expand_xsave_states(struct vcpu *v, void *dest, unsigned int size)
+void expand_xsave_states(const struct vcpu *v, void *dest, unsigned int size)
 {
     const struct xsave_struct *xsave = v->arch.xsave_area;
     const void *src;