ASoC: fsl_utils: Don't use plain integer as NULL pointer

Fix sparse warning:
sound/soc/fsl/fsl_utils.c:125:31: sparse: warning: Using plain integer as NULL pointer
sound/soc/fsl/fsl_utils.c:125:42: sparse: warning: Using plain integer as NULL pointer

Fixes: 7bad8125 ("ASoC: fsl_utils: Add function to handle PLL clock source")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1657192806-10569-1-git-send-email-shengjiu.wang@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/fsl_utils.c

@@ -122,7 +122,7 @@ void fsl_asoc_reparent_pll_clocks(struct device *dev, struct clk *clk,
 				  struct clk *pll8k_clk,
 				  struct clk *pll11k_clk, u64 ratio)
 {
-	struct clk *p, *pll = 0, *npll = 0;
+	struct clk *p, *pll = NULL, *npll = NULL;
 	bool reparent = false;
 	int ret = 0;