ath10k: remove extraneous error message in tx alloc

Remove extraneous error message in 'ath10k_htt_tx_alloc_cont_frag_desc'
as the caller 'ath10k_htt_tx_alloc' already dumps a proper error
message

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>