powerpc/boot: Add PROM_ERROR define in oflib

This is mostly useful to make to the boot wrapper code closer with
the kernel code in prom_init.

Signed-off-by: Cédric Le Goater <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/boot/of.h

···
 #define cpu_to_be32(x) (x)
 #define be32_to_cpu(x) (x)
 
+#define PROM_ERROR (-1u)
+
 #endif /* _PPC_BOOT_OF_H_ */

arch/powerpc/boot/oflib.c

···
 		args.args[nargs+i] = 0;
 
 	if (prom(&args) < 0)
-		return -1;
+		return PROM_ERROR;
 
 	return (nret > 0) ? be32_to_cpu(args.args[nargs]) : 0;
 }
···
 		args.args[nargs+i] = 0;
 
 	if (prom(&args) < 0)
-		return -1;
+		return PROM_ERROR;
 
-	if (rets != (void *) 0)
+	if (rets != NULL)
 		for (i = 1; i < nret; ++i)
 			rets[i-1] = be32_to_cpu(args.args[nargs+i]);