target-arm: Add missing 'static' attribute

This fixes a warning from the static code analysis (smatch).
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

target-arm/machine.c

@@ -88,7 +88,7 @@ static bool m_needed(void *opaque)
     return arm_feature(env, ARM_FEATURE_M);
 }
 
-const VMStateDescription vmstate_m = {
+static const VMStateDescription vmstate_m = {
     .name = "cpu/m",
     .version_id = 1,
     .minimum_version_id = 1,