media: tc358746: fix the pll calculating function

Following formula of Pll_clk in 5.2 section, 50th page of
TC358746AXBG/748XBG/748IXBG Functional Specification Rev 1.1 document.
The formula of fout is as below:
	fout = refclk * mul / (prediv * postdiv)

Remove "p" to avoid using 2 times of prediv in pll calculating function.

Signed-off-by: Duc-Long, Le <duclong.linux@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>