ARM: 8596/1: amba: Support clk parents and rates assigned in DT

Add the call to of_clk_set_defaults() into the amba probe path so
that devices on the amba bus can use the assigned rates and
parents feature of the common clock framework.

Cc: Michael Turquette <mturquette@baylibre.com>
Tested-by: Jorge Ramirez Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>