net/wan/fsl_ucc_hdlc: fix muram allocation error

sizeof(priv->ucc_pram) is 4 as it is the size of a pointer, but we want
to reserve space for the struct ucc_hdlc_param.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Cc: Zhao Qiang <qiang.zhao@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>