net: stmmac: imx: use stmmac_pltfr_probe()

Using stmmac_pltfr_probe() simplifies the probe function. This will not
only call plat_dat->init (imx_dwmac_init), but also plat_dat->exit
(imx_dwmac_exit) appropriately if stmmac_dvr_probe() fails. This
results in an overall simplification of the glue driver.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1u4Flp-000XlM-Tb@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>