scst: Let vfree handle absent verification and copy buffers

Coccinelle free/ifnullfree.cocci reports:

  scst/src/scst_lib.c:15441:2-7:
  WARNING: NULL check before some freeing functions is not needed.

Remove the redundant guard around vfree(buf) in scst_copy_file and the
same guard around vfree(mem_verify) in vdev_verify. Both pointers may be
NULL on cleanup paths, which vfree accepts throughout the supported
kernel range.

Leave the NULL guards in backport.h intact: they protect older teardown
APIs whose NULL handling differs, rather than these vfree calls.

scst/src/dev_handlers/scst_vdisk_main.c

@@ -2929,8 +2929,7 @@ static enum compl_status_e vdev_verify(struct scst_cmd *cmd, loff_t loff)
 	}
 
 out_free:
-	if (mem_verify)
-		vfree(mem_verify);
+	vfree(mem_verify);
 
 out:
 	TRACE_EXIT();

scst/src/scst_lib.c

@@ -15439,8 +15439,7 @@ out_close:
 	filp_close(file_src, NULL);
 
 out_free:
-	if (buf != NULL)
-		vfree(buf);
+	vfree(buf);
 
 out:
 	TRACE_EXIT_RES(res);