spi: atmel_spi: using ip version to check whether has wdrbt

Using IP version to check whether it has wdrbt bit in mode register

Tested in at91sam9x5ek and at91sam9n12ek.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
[fix warning about incompatible parameter]
Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>