ASoC: max98390: Fix incorrect printf qualifier

This patch addresses a compile warning:
  sound/soc/codecs/max98390.c:781:3: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 4 has type ‘size_t {aka const unsigned int}’ [-Wformat=]

Fixes: a6e3f4f3

 ("ASoC: max98390: Added Amplifier Driver")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200602164453.29925-1-tiwai@suse.de
Signed-off-by: Mark Brown <broonie@kernel.org>