Bluetooth: qca: fix firmware check error path

A recent commit fixed the code that parses the firmware files before
downloading them to the controller but introduced a memory leak in case
the sanity checks ever fail.

Make sure to free the firmware buffer before returning on errors.

Fixes: f905ae0be4b7 ("Bluetooth: qca: add missing firmware sanity checks")
Cc: stable@vger.kernel.org      # 4.19
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>