ASoC: wm8741: check for error returns from wm8741_set_pdata()

Static checkers complain that "ret" is always zero so the conditions are
never true.

The intention here was clearly to check for errors from
wm8741_set_pdata().  Although, since wm8741_set_pdata() never returns
errors, it doesn't affect runtime.

Fixes: c354b54c

 ('ASoC: wm8741: Add differential mono mode support')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>