clk: spear3xx: Use proper control register offset

The control register is at offset 0x10, not 0x0. This is wreckaged
since commit 5df33a62

 (SPEAr: Switch to common clock framework).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>