cutils: Drop broken support for zero strtosz default_suffix

Commit 9f9b17a4's strtosz() defaults a missing suffix to 'M', except
it rejects fractions then (switch case 0).

When commit d8427002 introduced strtosz_suffix(), that changed:
fractions are no longer rejected, because we go to switch case 'M' on
missing suffix now.  Not mentioned in commit message, probably
unintentional.  Not worth changing back now.

Because case 0 is still around, you can get the old behavior by
passing a zero default_suffix to strtosz_suffix() or
strtosz_suffix_unit().  Undocumented and not used.  Drop.

Commit d8427002 also neglected to update the function comment.  Fix it
up.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

cutils.c

@@ -317,10 +317,9 @@ int fcntl_setfl(int fd, int flag)
 
 /*
  * Convert string to bytes, allowing either B/b for bytes, K/k for KB,
- * M/m for MB, G/g for GB or T/t for TB. Default without any postfix
- * is MB. End pointer will be returned in *end, if not NULL. A valid
- * value must be terminated by whitespace, ',' or '\0'. Return -1 on
- * error.
+ * M/m for MB, G/g for GB or T/t for TB. End pointer will be returned
+ * in *end, if not NULL. A valid value must be terminated by
+ * whitespace, ',' or '\0'. Return -1 on error.
  */
 int64_t strtosz_suffix_unit(const char *nptr, char **end,
                             const char default_suffix, int64_t unit)
@@ -349,11 +348,7 @@ int64_t strtosz_suffix_unit(const char *nptr, char **end,
     d = c;
     if (qemu_isspace(c) || c == '\0' || c == ',') {
         c = 0;
-        if (default_suffix) {
-            d = default_suffix;
-        } else {
-            d = c;
-        }
+        d = default_suffix;
     }
     switch (qemu_toupper(d)) {
     case STRTOSZ_DEFSUFFIX_B:
@@ -365,10 +360,6 @@ int64_t strtosz_suffix_unit(const char *nptr, char **end,
     case STRTOSZ_DEFSUFFIX_KB:
         mul = unit;
         break;
-    case 0:
-        if (mul_required) {
-            goto fail;
-        }
     case STRTOSZ_DEFSUFFIX_MB:
         mul = unit * unit;
         break;