Use mdelay instead of udelay to fix this error:

ERROR: "__bad_udelay" [drivers/net/wireless/ath/ath9k/ath9k_hw.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2
Reported-by: NJosh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: NSujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>