MIPS: Octeon: Remove bogus code from octeon_get_clock_rate()

We can run with any simulator clock rate.  Get rid of the code
overriding it to 6MHz.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Patchwork: http://patchwork.linux-mips.org/patch/1669/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>