staging: et131x: fix invalid fail after the call to eeprom_wait_ready

should be err < 0 instead of if (err) which actually the read register
value can be a positive number

Acked-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>