bt: avoid unintended sign extension

In the case of a 4-byte length, shifting a value by 24 may cause
an unintended sign extension when converting from int to size_t.
Use a uint32_t variable instead.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/bt/sdp.c

@@ -42,7 +42,7 @@ struct bt_l2cap_sdp_state_s {
 
 static ssize_t sdp_datalen(const uint8_t **element, ssize_t *left)
 {
-    size_t len = *(*element) ++ & SDP_DSIZE_MASK;
+    uint32_t len = *(*element) ++ & SDP_DSIZE_MASK;
 
     if (!*left)
         return -1;