gpu: nova-core: use checked arithmetic in BinFirmware::data

Use checked_add() when computing the firmware data end offset in the
BinFirmware::data() method. The data_offset and data_size fields come
from the BinHdr structure parsed from the firmware file header.

Reviewed-by: Zhi Wang <zhiw@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>