Bluetooth: qca: fix info leak when fetching fw build id

Add the missing sanity checks and move the 255-byte build-id buffer off
the stack to avoid leaking stack data through debugfs in case the
build-info reply is malformed.

Fixes: c0187b0b

 ("Bluetooth: btqca: Add support to read FW build version for WCN3991 BTSoC")
Cc: stable@vger.kernel.org	# 5.12
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>