Fix the freqsel value computation. Use n instead of (n+1)

The formula in the TRM uses a zero-based N, hence the (n+1); however
at this point in the clock34xx.c code, N is one-based.

Hayati Bayrakdar <h-bayrakdar@ti.com> and Nishanth Menon <nm@ti.com> helped
track down this bug.
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
[paul@pwsan.com: modified commit message]
Cc: Hayati Bayrakdar <h-bayrakdar@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>