Spur frequency was incorrectly computed with 10Mhz offset
which could cause the filter would not notch out the spur
and also this could improve rx sensitivity in HT40.

Cc: Madhan Jaganathan <madhanj@qca.qualcomm.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>