[PATCH] x86: restore semicolon after explicit DS prefix

[Jan Beulich]

It's not unnecessary (as the earlier commit claimed): The integrated
assembler of Clang up to 11 complains about an "invalid operand for
instruction".

Fixes: b42cf31d1165 ("x86: use alternative_input() in cache_flush()")
Signed-off-by: Jan Beulich <jbeul...@suse.com>

--- a/xen/arch/x86/flushtlb.c
+++ b/xen/arch/x86/flushtlb.c
@@ -286,7 +286,7 @@ void cache_flush(const void *addr, unsig
          * + prefix than a clflush + nop, and hence the prefix is added instead
          * of letting the alternative framework fill the gap by appending nops.
          */
-        alternative_input("ds clflush %[p]",
+        alternative_input("ds; clflush %[p]",
                           "data16 clflush %[p]", /* clflushopt */
                            X86_FEATURE_CLFLUSHOPT,
                            [p] "m" (*(const char *)(addr)));