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>
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 34ddba0..8e6272c 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -643,7 +643,7 @@
     FSFREEZE_HOOK_FREEZE,
 } FsfreezeHookArg;
 
-const char *fsfreeze_hook_arg_string[] = {
+static const char *fsfreeze_hook_arg_string[] = {
     "thaw",
     "freeze",
 };