ath10k: remove impossible code

len has been initialized with a value of 0 and buf_len with 4096. There
is no way that this condition (len > buf_len) can be true now.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>