ath10k: replace bit shifts with the BIT() macro for rx desc bits

Use the BIT() macro from 'linux/bitops.h' to define the rx desc
bit flags to have consistency with new definitions.

Signed-off-by: Govind Singh <govinds@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>