xen/common: llc-coloring: Fix off-by-one in parse_color_config()

The check uses (*num_colors + (end - start + 1)) >= max_num_colors, which
rejects a configuration where exactly max_num_colors colors are specified.
For example, if max_num_colors is 4 and *num_colors is 0, a range "0-3"
gives (end - start + 1) = 4, and (0 + 4) >= 4 is true, incorrectly
returning -EINVAL.

Fix this by switching the overflow condition to the state before commit
cba8a584de that regressed the behavior (i.e. don't add 1).

Fixes: cba8a584de ("llc-coloring: improve checking while parsing")
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>

xen/common/llc-coloring.c

@@ -78,7 +78,7 @@ static int __init parse_color_config(const char *buf, unsigned int colors[],
 
         if ( end >= NR_LLC_COLORS || start > end ||
              (end - start) >= (UINT_MAX - *num_colors) ||
-             (*num_colors + (end - start + 1)) >= max_num_colors )
+             (*num_colors + (end - start)) >= max_num_colors )
             return -EINVAL;
 
         /* Colors are range checked in check_colors() */