gpu: nova-core: use checked arithmetic in RISC-V firmware parsing

gpu: nova-core: use checked arithmetic in RISC-V firmware parsing

Use checked_add() when computing offsets from firmware-provided values
in the RISC-V firmware parsing code. These values 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>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260126202305.2526618-6-joelagnelf@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>