clk: tegra: Fix 26 MHz oscillator frequency

The OSC_FREQ field of the OSC_CTRL register uses the value 12 for an
oscillator frequency of 26 MHz, not 260 MHz. This isn't really critical
because I don't think boards with such an oscillator have ever existed,
much less been supported upstream.

Signed-off-by: Thierry Reding <treding@nvidia.com>