sparc: Compare pointers to NULL instead of 0

Fixes the following two Coccinelle/coccicheck warnings reported by
badzero.cocci:

	WARNING comparing pointer to 0
	WARNING comparing pointer to 0
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240404192932.13075-2-thorsten.blum@toblux.comSigned-off-by: Andreas Larsson <andreas@gaisler.com>

arch/sparc/prom/tree_64.c

@@ -332,7 +332,7 @@ prom_setprop(phandle node, const char *pname, char *value, int size)
 
 	if (size == 0)
 		return 0;
-	if ((pname == 0) || (value == 0))
+	if ((pname == NULL) || (value == NULL))
 		return 0;
 	
 #ifdef CONFIG_SUN_LDOMS