drm/appletbdrm: Fix ref-counting on dmadev

Remove the put_device() call on dmadev. The driver sets the field
without getting a reference, so it shouldn't put a reference either.
The dmadev field points to the regular USB device for which DRM
maintains a reference internally. Hence dmadev will not become dangling
during the DRM device's lifetime.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 0670c2f5 ("drm/tiny: add driver for Apple Touch Bars in x86 Macs")
Cc: Aditya Garg <gargaditya08@live.com>
Cc: Aun-Ali Zaidi <admin@kodeit.net>
Cc: dri-devel@lists.freedesktop.org
Acked-by: Aditya Garg <gargaditya08@live.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250307083702.142675-1-tzimmermann@suse.de