msm_serial: fix serial on trout

Set the mnd counter based on uartclk. This fixes a problem
on 7x30 where the uartclk is 19.2Mhz rather than the usual
4.8Mhz.

Trout incorrectly reports uartclk to be running at 19.2Mhz
It is actually running at 4.8Mhz.  For trout force mnd
counter values as if uartclk was fed by tcxo/4.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
[dwalker@codeaurora.org: inlined, moved into header, added comments.]
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>