gpu: nova-core: use sized array for GSP log buffers

gpu: nova-core: use sized array for GSP log buffers

Switch LogBuffer from Coherent<[u8]> (unsized) to
Coherent<[u8; LOG_BUFFER_SIZE]> (sized). The buffer size is a
compile-time constant (RM_LOG_BUFFER_NUM_PAGES * GSP_PAGE_SIZE), so a
fixed-size array is more precise and avoids the need for the runtime
length parameter of zeroed_slice().

Acked-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260325003921.3420-3-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>