ath10k: remove redundant check of len with buf_len

The check of len > buf_len is redundant as len is initialized
to 0 and buf_len to 4096, so this comparison is always false.
Remove it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>