ns16550: change reg-shift property default to zero

Change reg-shift property default to zero. When the integer property
is missing, it should be taken as zero. This is consistent to Linux
drivers/tty/serial/of_serial.c.

The x86 and most powerpc use reg-shift of 0. Most others use reg-shift
of 2. While reg-shift of 1 is rarely used.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Simon Glass <sjg@chromium.org>

drivers/serial/ns16550.c

@@ -403,7 +403,7 @@ int ns16550_serial_ofdata_to_platdata(struct udevice *dev)
 
 	plat->base = addr;
 	plat->reg_shift = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
-					 "reg-shift", 1);
+					 "reg-shift", 0);
 	plat->clock = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
 				     "clock-frequency",
 				     CONFIG_SYS_NS16550_CLK);