tty: serial: msm: Remove 115.2 Kbps maximum baud rate limitation

UART controller is capable to perform transfers up to 4 Mbps.
Remove artificial 115.2 Kbps limitation.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>