cifsd: fix invalid memory access in smb2_write()

Add missing fp initialzation to prevent invalid memory access in
smb2_write().

Reported-by: Coverity Scan <scan-admin@coverity.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/smb2pdu.c

@@ -6078,7 +6078,7 @@ int smb2_write(struct ksmbd_work *work)
 {
  struct smb2_write_req *req;
  struct smb2_write_rsp *rsp, *rsp_org;
- struct ksmbd_file *fp;
+ struct ksmbd_file *fp = NULL;
  loff_t offset;
  size_t length;
  ssize_t nbytes;