serial: MPSC: set baudrate when BRG divider is set.

The clock to generate the desired baudrate with the MPSC is first divided
by the Baud Rate Generator (BRG) and then by the MPSC itself.  So, when the
BRG divider is changed, the MPSC divider must also be changed to generate
the correct baudrate.  During MPSC initialization, the BRG divider is
changed but the MPSC divider isn't changed until much later.  This results
in some printk's coming out garbled.  To fix that, set the MPSC divider at
the same time that the BRG divider is changed.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>