ath10k: use octal permission representation

Fix output from checkpatch.pl like:
 Symbolic permissions 'S_IRUSR' are not preferred.
 Consider using octal permissions '0400'.

Signed-off-by: Marcin Rokicki <marcin.rokicki@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>