clk: pxa: b bit of clkcfg means fast bus

The meaning of this bit was inverted :
 - when set to 0, system bus clock is half of the CPU run clock
 - when set to 1, system bus clock is the CPU run clock

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>