nfc: s3fwrn5: Constify s3fwrn5_fw_info when not modified

Two functions accept pointer to struct s3fwrn5_fw_info but do not
modify the contents.  Make them const so the code is a little bit safer.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>