tty: serial: qcom_geni_serial: Update the oversampling rate

For QUP IP versions 2.5 and above the oversampling rate is halved
from 32 to 16. Update this rate after reading hardware version
register, so that the clock divider value is correctly set to
achieve required baud rate.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Link: https://lore.kernel.org/r/20190801121153.10613-1-vivek.gautam@codeaurora.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>