clk: qcom: Fix pre-divider usage for pixel RCG

The clk_rcg_pixel_set_rate clk_op sets up the pre-divider by reading
its current value from the NS register.

Using the pre-divider wasn't really intended when creating these ops.
The pixel RCG was only intended to achieve fractional multiplication
provided in the pixel_table array. Leaving the pre-divider to the
existing register value results in a wrong pixel clock when the
bootloader sets up the display. This was left unidentified because
the IFC6410 Plus board on which this was verified didn't have a
bootloader that configured the display.

Don't set the RCG pre-divider in freq_tbl to the existing NS register
value. Force it to 1 and only use the M/N counter to achieve the desired
fractional multiplication.

Cc: Vinay Simha <vinaysimha@inforcecomputing.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>