mmc: omap_hsmmc: correct max value of clkd

clock divisor can take a max value of 1023.  Update code so that card
init can be handled at f_min even at higher IP clock frequencies from
which clock to the card is derived.

Signed-off-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>