nvme-fcloop: Fix sscanf type and list_first_entry_or_null warnings

Kernel robot had the following warnings:

>> fcloop.c:1506:6: warning: %x in format string (no. 1) requires
>> 'unsigned int *' but the argument type is 'signed int *'.
>> [invalidScanfArgType_int]
>>    if (sscanf(buf, "%x:%d:%d", &opcode, &starting, &amount) != 3)
>>        ^

Resolve by changing opcode from and int to an unsigned int

and

>>  fcloop.c:1632:32: warning: Uninitialized variable: lport [uninitvar]
>>     ret = __wait_localport_unreg(lport);
>>                                  ^

>>  fcloop.c:1615:28: warning: Uninitialized variable: nport [uninitvar]
>>     ret = __remoteport_unreg(nport, rport);
>>                              ^

These aren't actual issues as the values are assigned prior to use.
It appears the tool doesn't understand list_first_entry_or_null().
Regardless, quiet the tool by initializing the pointers to NULL at
declaration.
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/fcloop.c

@@ -1501,7 +1501,8 @@ static ssize_t
 fcloop_set_cmd_drop(struct device *dev, struct device_attribute *attr,
 		const char *buf, size_t count)
 {
-	int opcode, starting, amount;
+	unsigned int opcode;
+	int starting, amount;
 
 	if (sscanf(buf, "%x:%d:%d", &opcode, &starting, &amount) != 3)
 		return -EBADRQC;
@@ -1588,8 +1589,8 @@ static int __init fcloop_init(void)
 
 static void __exit fcloop_exit(void)
 {
-	struct fcloop_lport *lport;
-	struct fcloop_nport *nport;
+	struct fcloop_lport *lport = NULL;
+	struct fcloop_nport *nport = NULL;
 	struct fcloop_tport *tport;
 	struct fcloop_rport *rport;
 	unsigned long flags;