staging: mt7621-dma: Fix a resource leak in an error handling path

staging: mt7621-dma: Fix a resource leak in an error handling path

If an error occurs after calling 'mtk_hsdma_init()', it must be undone by
a corresponding call to 'mtk_hsdma_uninit()' as already done in the
remove function.

Fixes: 0853c7a53eb3 ("staging: mt7621-dma: ralink: add rt2880 dma engine")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201213153513.138723-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>