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>