Bluetooth: qca: add missing firmware sanity checks

Add the missing sanity checks when parsing the firmware files before
downloading them to avoid accessing and corrupting memory beyond the
vmalloced buffer.

Fixes: 83e81961

 ("Bluetooth: btqca: Introduce generic QCA ROME support")
Cc: stable@vger.kernel.org	# 4.10
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>