prov/verbs: Fix compiler warning on the bound of 'strncpy' call

Gcc 15 complains that the length parameter for strncpy() is derived from
the source string. It is not a real concern since the result is guaranteed
to be less than the buffer size due to the MIN operation. However, the
calculation is slightly off anyway. So rewite the logic to kill two birds
with one stone.

Signed-off-by: Jianxin Xiong <[email protected]>

Author: j-xiong

prov/verbs/src/verbs_init.c

@@ -374,12 +374,9 @@ static int vrb_param_define(const char *param_name, const char *param_str,
 		switch (type) {
 		case FI_PARAM_STRING:
 			if (*(char **)param_default != NULL) {
-				param_default_sz =
-					MIN(strlen(*(char **)param_default),
-					    254);
-				strncpy(param_default_str, *(char **)param_default,
-					param_default_sz);
-				param_default_str[param_default_sz + 1] = '\0';
+				strncpy(param_default_str, *(char **)param_default, 255);
+				param_default_str[255] = '\0';
+				param_default_sz = strlen(param_default_str);
 			}
 			break;
 		case FI_PARAM_INT: