ath10k: fix ath10k_bmi_read32 macro

tmp may be used uninitialized if ath10k_bmi_read_memory() returns
an error.

Signed-off-by: Frederic Danis <frederic.danis@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>