clk: pxa: fix core frequency reporting unit

Legacy drivers which are not yet ported, such as cpufreq-pxa[23]xx, rely
on pxaXXx_get_clk_frequency_khz() to find the CPU core frequency.

This reporting was broken because the expected unit is kHz and not
Hz. Fix the reporting for pxa25x, pxa27x and pxa3xx.

Fixes: fe7710fa ("clk: add pxa25x clock drivers")
Fixes: d40670dc ("clk: add pxa27x clock drivers")
Fixes: 9bbb8a33 ("clk: pxa: add pxa3xx clock driver")
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>