net: wan/fsl_ucc_hdlc: Fix dma_free_coherent() in uhdlc_memclean()

net: wan/fsl_ucc_hdlc: Fix dma_free_coherent() in uhdlc_memclean()

The priv->rx_buffer and priv->tx_buffer are alloc'd together as
contiguous buffers in uhdlc_init() but freed as two buffers in
uhdlc_memclean().

Change the cleanup to only call dma_free_coherent() once on the whole
buffer.

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Fixes: c19b6d246a35 ("drivers/net: support hdlc function for QE-UCC")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Link: https://patch.msgid.link/20260206085334.21195-2-fourier.thomas@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>