scsi: target: configfs: Delete unnecessary checks for NULL

The "item" pointer is always going to be valid pointer and does not need to
be checked.

But if "item" were NULL then item_to_lun() would not return a NULL, but
instead, the container_of() pointer math would return a value in the error
pointer range.  This confuses static checkers since it looks like a NULL vs
IS_ERR() bug.

Delete the bogus checks.

Link: https://lore.kernel.org/r/20211118084900.GA24550@kili


Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>