ASoC: Fix warning caused by a typo in comments of snd_soc_add_platform()

This patch fix following warnings.
Warning(.//sound/soc/soc-core.c:2855): No description found
for parameter 'platform_drv'
Warning(.//sound/soc/soc-core.c:2855): Excess function parameter
'platform_driver' description in 'snd_soc_add_platform'

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>