nfc: mrvl: correct nfcmrvl_spi_parse_dt() device_node argument

The device_node in nfcmrvl_spi_parse_dt() cannot be const as it is
passed to OF functions which modify it.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>