x86/altcall: hide casting away of const

ALT_CALL_PTR() really means to get rid of const (when necessary, i.e. when
used from apply_alt_calls()): We want to patch the original call site,
after all, and memory-wise that's unrelated to the struct alt_call * that
we start from.

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger@xenproject.org>

xen/arch/x86/include/asm/alternative-call.h

@@ -9,7 +9,7 @@
 struct alt_call {
     int32_t offset;
 };
-#define ALT_CALL_PTR(a) ((void *)&(a)->offset + (a)->offset)
+#define ALT_CALL_PTR(a) ((void *)((long)&(a)->offset + (a)->offset))
 #define ALT_CALL_LEN(a) (6)
 
 /*