realtek: rt-loader: fix chip revision printout

realtek: rt-loader: fix chip revision printout

There is currently a mismatch in the detection of the chip type.
rt-loader and the kernel give different revisions. E.g.

rt-loader: Running on RTL9313 (chip id 6567A) with 256MB
kernel: Realtek RTL9313 rev B (6567) SoC with 256 MB

Realtek internal version numbering is

- for RTL838x: 1=A, 2=B, ...
- for others: 0=A, 1=B, ...

rt-loader does not differentiate that. Adapt the calculation to
give a consistent picture.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/21498
Signed-off-by: Robert Marko <robimarko@gmail.com>