clk: qcom: rcg2: Add DIV_ROUND_CLOSEST_ULL to roundoff RCG frequency

The Alpha BW for Fabia PLL is 16 bit and the calculated hw rate has 
additional KHz of frequency. Due to this additional frequency, the
source is wrongly selected. Truncate the additional KHz using the
DIV_ROUND_CLOSEST_ULL.

Change-Id: Ic9c523c87277c4813b676cf8a52a1207e8f1ecc2
Signed-off-by: Shefali Jain <shefjain@codeaurora.org>