qga: Add missing 'static' attribute

This fixes a warning from the static code analysis (smatch).

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

qga/commands-posix.c

@@ -643,7 +643,7 @@ typedef enum {
     FSFREEZE_HOOK_FREEZE,
 } FsfreezeHookArg;
 
-const char *fsfreeze_hook_arg_string[] = {
+static const char *fsfreeze_hook_arg_string[] = {
     "thaw",
     "freeze",
 };