OMAPDSS: DSI: Fix bug when calculating LP command interleaving parameters

In function dsi_compute_interleave_lp(), the escape clock/LP clock time period
is calculated incorrectly. The escape clock/LP clock is calculated as:

LP Clock(Hz) = DSI_FCLK(Hz) / lp_clk_div

Since we are calculating the time period of LP clock, the LP clock divider
should be multiplied with the time period of DSI_FCLK.

Calculating incorrect value of txclkesc results in incorrect calculation of LP
interleaving parameters, it also creates a possibility of a divide by zero
error.

Reported-by: Sureshkumar Manimuthu <mail2msuresh@ti.com>
Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>