ASoC: pxa-ssp: drop SNDRV_PCM_FMTBIT_S24_LE

commit 9301503af016eb537ccce76adec0c1bb5c84871e upstream.

This mode is unsupported, as the DMA controller can't do zero-padding
of samples.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Reported-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>