ASoC: tas2780: Fix set_tdm_slot in case of single slot

ASoC: tas2780: Fix set_tdm_slot in case of single slot

There's a special branch in the set_tdm_slot op for the case of nslots
being 1, but:

 (1) That branch can never work (there's a check for tx_mask being
     non-zero, later there's another check for it *being* zero; one or
     the other always throws -EINVAL).

 (2) The intention of the branch seems to be what the general other
     branch reduces to in case of nslots being 1.

For those reasons remove the 'nslots being 1' special case.

Fixes: eae9f9ce181b ("ASoC: add tas2780 driver")
Suggested-by: Jos Dehaes <jos.dehaes@gmail.com>
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20221027095800.16094-3-povik+lin@cutebit.org
Signed-off-by: Mark Brown <broonie@kernel.org>