gpu: nova-core: vbios: avoid reading too far in read_more_at_offset

gpu: nova-core: vbios: avoid reading too far in read_more_at_offset

Fix bug where `read_more_at_offset` would unnecessarily read more data.
This happens when the window to read has some part cached and some part
not. It would read `len` bytes instead of just the uncached portion,
which could read past `BIOS_MAX_SCAN_LEN`.

Fixes: 6fda04e7f0cd ("gpu: nova-core: vbios: Add base support for VBIOS construction and iteration")
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260525-fix-vbios-v5-3-e5e455251537@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>