phy: miphy365x: Fix off-by-one error

We index the RX/TX speed select values in the following way:

  rx_tx_spd[miphy_phy->sata_gen];

However rx_tx_spd[] starts at index zero and the SATA_GENx's start
at one.  In this patch we pad out the first element in rx_tx_spd[]
in an attempt to realign the values.

Cc: Alexandre Torgue <alexandre.torgue@st.com>
Reported-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>