We allocated memory for wm8731 in wm8731_spi_probe / wm8731_i2c_probe,
and will free the memory in either wm8731_spi_probe / wm8731_i2c_probe
error path or wm8731_spi_remove / wm8731_i2c_remove.

Thus we should not call kfree(wm8731) in wm8731_probe, otherwise
we have double free of wm8731.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>