prom_getchar eats characters

prom_getchar eats characters

This bug has been annoying me for a long time. If you copy and paste a
string into the yaboot prompt, or even type too fast, characters get
dropped.

It turns out we were asking OF for 4 characters, but only using the first one.
There is strange logic to look for \e[, and then oring the third character with
0x100. I haven't been able to find anyone that knows why that was there in the
first place, so just remove it and fix this bug once and for all.

Automated test infrastructures the world over will thank us for fixing this
bug!

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>