ethernet: sun: niu: fix missing checks of niu_pci_eeprom_read()

ethernet: sun: niu: fix missing checks of niu_pci_eeprom_read()

niu_pci_eeprom_read() may fail, so add checks to its return value and
propagate the error up the callstack.

An examination of the callstack up to niu_pci_eeprom_read shows that:

niu_pci_eeprom_read() // returns int
    niu_pci_vpd_scan_props() // returns int
        niu_pci_vpd_fetch() // returns *void*
            niu_get_invariants() // returns int

since niu_pci_vpd_fetch() returns void which breaks the bubbling up,
change its return type to int so that error is propagated upwards.

Signed-off-by: Du Cheng <ducheng2@gmail.com>
Cc: Shannon Nelson <shannon.lee.nelson@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210503115736.2104747-24-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>