serial: 8250_mtk: make two read-only arrays static const

Don't populate the read-only arrays fraction_L_mapping and
fraction_M_mapping on the stack but instead make them static
const. Also makes the object code a little smaller.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220307230055.168241-1-colin.i.king@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>