MIPS: Netlogic: Fix frequency calculation register

Change the PIC frequency calculation to use the register that has the
current configuration. The existing code used the register that is
written to change frequency, which can have an invalid value if the
firmware did not set it up correctly.

Signed-off-by: Ganesan Ramalingam <ganesanr@broadcom.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8885/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>