of: align RESERVEDMEM_OF_DECLARE function callbacks to other callbacks

All the parameters for RESERVEDMEM_OF_DECLARE function callbacks are
members of struct reserved_mem, so just pass the struct ptr to callback
functions so the function callback is more in line with other OF match
table callbacks.

Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>