nvmecontrol wdc: Don't pass a bogus pointer to free().

[jhb]

Summary

wdc_get_dui_log_size allocates a buffer and then advances the
returned pointer. Passing this advanced pointer to free() is UB,
so save the original pointer to pass to free() instead.

Reported by: GCC 12 -Wfree-nonheap-object

sbin/nvmecontrol/modules/wdc/wdc.c

 .El
 .Ss Netgraph Message Structure
 Control messages have the following structure:
 .Bd -literal
 #define NG_CMDSTRSIZ    32      /* Max command string (including null) */
 
 struct ng_mesg {
   struct ng_msghdr {
-    u_char      version;        /* Must equal NG_VERSION */
+    u_char      version;        /* Must equal NGM_VERSION */
     u_char      spare;          /* Pad to 4 bytes */
     uint16_t    spare2;
     uint32_t    arglen;         /* Length of cmd/resp data */
     uint32_t    cmd;            /* Command identifier */
     uint32_t    flags;          /* Message status flags */
     uint32_t    token;          /* Reply should have the same token */
     uint32_t    typecookie;     /* Node type understanding this message */
     u_char      cmdstr[NG_CMDSTRSIZ];  /* cmd string + \0 */
   } header;
   char  data[];                 /* placeholder for actual data */
 };
 
 #define NG_ABI_VERSION  12              /* Netgraph kernel ABI version */
-#define NG_VERSION      8               /* Netgraph message version */
-#define NGF_ORIG        0x00000000      /* The msg is the original request */
+#define NGM_VERSION     8               /* Netgraph message version */
 #define NGF_RESP        0x00000001      /* The message is a response */
 .Ed
 .Pp
 Control messages have the fixed header shown above, followed by a
 variable length data section which depends on the type cookie
 and the command.
 Each field is explained below:
 .Bl -tag -width indent
 .It Va version
 Indicates the version of the
 .Nm
 message protocol itself.
 The current version is
-.Dv NG_VERSION .
+.Dv NGM_VERSION .
 .It Va arglen
 This is the length of any extra arguments, which begin at
 .Va data .
 .It Va flags
 Indicates whether this is a command or a response control message.
 .It Va token
 The
 .Va token