Fix two minor lint errors (cppcheck)

Fix two minor errors reported by cppcheck:

In module/zfs/abd.c (abd_get_offset_impl), add non-NULL
assertion to prevent NULL dereference warning.

In module/zfs/arc.c (l2arc_write_buffers), change 'try'
variable to 'pass' to avoid C++ reserved word.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Colm Buckley <colm@tuatha.org>
Closes #11507

module/zfs/abd.c

@@ -526,6 +526,7 @@ abd_get_offset_impl(abd_t *abd, abd_t *sabd, size_t off, size_t size)
 		abd = abd_get_offset_scatter(abd, sabd, off);
 	}
 
+	ASSERT3P(abd, !=, NULL);
 	abd->abd_size = size;
 	abd->abd_parent = sabd;
 	(void) zfs_refcount_add_many(&sabd->abd_children, abd->abd_size, abd);