ath6kl: Remove useless initialization in ath6kl_read_fwlogs()

ath6kl_read_fwlogs() assigns the value zero to the variable 'ret'
at the time of declaration. Later, return value of ath6kl_diag_read32()
repalces the init value. Hence removing useless zero assignment.

Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>