usb: Use g_new() & friends where that makes obvious sense

g_new(T, n) is neater than g_malloc(sizeof(T) * n).  It's also safer,
for two reasons.  One, it catches multiplication overflowing size_t.
Two, it returns T * rather than void *, which lets the compiler catch
more type errors.

This commit only touches allocations with size arguments of the form
sizeof(T).  Same Coccinelle semantic patch as in commit b45c03f.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/usb/dev-mtp.c

@@ -359,8 +359,7 @@ static void usb_mtp_object_readdir(MTPState *s, MTPObject *o)
     }
     while ((entry = readdir(dir)) != NULL) {
         if ((o->nchildren % 32) == 0) {
-            o->children = g_realloc(o->children,
-                                    (o->nchildren + 32) * sizeof(MTPObject *));
+            o->children = g_renew(MTPObject *, o->children, o->nchildren + 32);
         }
         o->children[o->nchildren] =
             usb_mtp_object_alloc(s, s->next_handle++, o, entry->d_name);