ath10k: free cached fw bin contents when get board id fails

ath10k_core_probe_fw() simply returns error without freeing
cached firmware file content when get board id operation fails.
Free cached fw bin data in failure case to avoid memory leak.

Fixes: db0984e5 ("ath10k: select board data based on BMI chip id and board id")
Signed-off-by: Raja Mani <rmani@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>