cypress_m8: switch data_bits to real character bits

Make data_bits what it really is. Assign proper bit counts to data_bits
instead of magic 0..3. There are two reasons:
1) it's clear what we store there, and
2) it will make the transition to tty_tty_get_char_size() in the next
   patch easier.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210610090247.2593-3-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>