Fix cppcheck warning:

sound/drivers/vx/vx_pcm.c:539:30: style: Variable
'chip->playback_pipes[audio]' is reassigned a value before the old one
has been used. [redundantAssignment]
 chip->playback_pipes[audio] = pipe;
                             ^
sound/drivers/vx/vx_pcm.c:533:31: note: chip->playback_pipes[audio] is
assigned
  chip->playback_pipes[audio] = pipe;
                              ^
sound/drivers/vx/vx_pcm.c:539:30: note: chip->playback_pipes[audio] is
overwritten
 chip->playback_pipes[audio] = pipe;
                             ^
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200902212133.30964-18-pierre-louis.bossart@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>