linux-phytec-ti

ath9k: fix TSF offset precision issue

Dividing the beacon interval by ATH_BCBUF (8) truncates the result for
the default beacon interval of 100.
Fix the calculation by moving the division after conversion from TU to
microseconds.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>