vt: use min() to limit intervals

Instead of awkward ternary operator with comparison, use simple min()
for blankinterval and vesa_off_interval.

No functional change intended and "objdump -d" proves that.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200316065911.11024-1-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>