net: stmmac: anarion: clean up anarion_config_dt() error handling

net: stmmac: anarion: clean up anarion_config_dt() error handling

When enabled, print a user friendly description of the error when
failing to ioremap() the control resource, and use ERR_CAST() when
propagating the error. This allows us to get rid of the "err" local
variable in anarion_config_dt().

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1u4FlQ-000XjA-2V@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>