1. In cfi_write_unalign(): Add additional check to ensure nbytes is
at least bankwidth size before skipping unaligned start handling.
This prevents incorrect behavior when writing small amounts of
data that are less than bankwidth.
2. In cfi_write(): Align down the write size to bankwidth boundary
when the remaining nbytes is less than the buffer write size.
This ensures the buffer write operation always works with properly
aligned data size, preventing write failures.))
Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>