HID: magicmouse: avoid memory leak in magicmouse_report_fixup()

HID: magicmouse: avoid memory leak in magicmouse_report_fixup()

The magicmouse_report_fixup() function was returning a
newly kmemdup()-allocated buffer, but never freeing it.

The caller of report_fixup() does not take ownership of the returned
pointer, but it *is* permitted to return a sub-portion of the input
rdesc, whose lifetime is managed by the caller.

Assisted-by: Gemini-CLI:Google Gemini 3
Signed-off-by: Günther Noack <gnoack@google.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>