mxs-auart: redefine AUART_LINECTRL_WLEN to accept bits count

mxs-auart: redefine AUART_LINECTRL_WLEN to accept bits count

It's a bit illogical to take magic constants in AUART_LINECTRL_WLEN.
Like in auart_console_get_options(), 2 means 7 bits. Switch
AUART_LINECTRL_WLEN to accept bit length, i.e. let it subtract 5 from
the parameter before doing the logic.

This will ease conversion from CSIZE to bits in mxs_auart_settermios()
in the next patch.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210610090247.2593-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>