test: Adjust print_ut test to use unsigned char

test: Adjust print_ut test to use unsigned char

Since char is unsigned on arm64, this test currently fails. It seems
better to use unsigned anyway, since 0xff is written into the string at
the start. Update the terminator-assert to use a character instead of a
byte.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Changes in v6:
- Re-introduce

Changes in v2:
- Use '\0' instead of 0

test/print_ut.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)