clk: mvebu: Fix valid value range checking for cpu_freq_select

cpu_freq_select is used as array subscript, thus the valid value range
is 0 ... ARRAY_SIZE() - 1.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: fixed up trivial merge issues]