serial: goldfish: return error when device address is invalid

serial: goldfish: return error when device address is invalid

goldfish_serial_of_to_plat() returns success even when dev_read_addr()
fails to find a valid address. This leaves plat->reg unset and defers
the failure to probe().

Return -EINVAL immediately when the address is FDT_ADDR_T_NONE so the
failure is reported at the of_to_plat stage where it belongs.

Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
Acked-by: Kuan-Wei Chiu <visitorckw@gmail.com>