staging: hikey9xx: Fix incorrect assignment

staging: hikey9xx: Fix incorrect assignment

In hi3670_phy_probe(), when reading property tx-vboost-lvl fails, its
default value is assigned to priv->eye_diagram_param, rather than to
priv->tx_vboost_lvl. Fix this.

Fixes: 8971a3b880b2 ("staging: hikey9xx: add USB physical layer for Kirin 3670")
Addresses-Coverity: CID 1497107: Incorrect expression (COPY_PASTE_ERROR)
Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Link: https://lore.kernel.org/r/20200921212146.34662-1-alex.dewar90@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>