omap2 clock: vlynq_fck recalc should be clksel, not followparent

vlynq_fck is a clksel clock, so its rate is equal to its parent's
rate, divided by whichever divisor is selected.  But its definition in
clock.h specifies omap2_followparent_recalc() as its rate calculation
code, which sets the clock's rate to that of its parent without
accounting for any divisor.  Fix to use omap2_clksel_recalc() instead.
omap2_clksel_recalc() is also missing the appropriate special case to
divide the vlynq_fck rate down; add this in.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>