Remove the duplicate checking of TX ring's available number, and remove
the variable to store available number that can be calculated by
read/write pointers.
Signed-off-by: Steven Ting <steventing@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>