MIPS: Netlogic: Fix nlm_xlp2_get_pic_frequency to use ref_div

MIPS: Netlogic: Fix nlm_xlp2_get_pic_frequency to use ref_div

The variable ref_div is initialized to the correct divisor but not
used in the frequency calculation. This caused incorrect frequency
to be reported when the clock divisor is not 3.

Signed-off-by: Qingmin Liu <qingmin@broadcom.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8884/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>