clk: imx: composite-7ulp: Use NULL instead of 0

Address the sparse warnings "
sparse warnings: (new ones prefixed by >>)
>> drivers/clk/imx/clk-composite-7ulp.c:85:24: sparse: sparse:
Using plain integer as NULL pointer
"

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Peng Fan <[email protected]>
Reviewed-by: Abel Vesa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Abel Vesa <[email protected]>

Author: MrVan

drivers/clk/imx/clk-composite-7ulp.c

@@ -82,7 +82,7 @@ static struct clk_hw *imx_ulp_clk_hw_composite(const char *name,
 	val = readl(reg);
 	if (!(val & PCG_PR_MASK)) {
 		pr_info("PCC PR is 0 for clk:%s, bypass\n", name);
-		return 0;
+		return NULL;
 	}
 
 	if (mux_present) {