dm: avoid NULL dereference in lists_bind_fdt()

If parameter drv of lists_bind_fdt() is specified, we want to bind to this
specific driver even if its field of_match is NULL.

If entry->of_match is NULL, we should not dereference it in a debug
statement.

Fixes: d3e77361 ("dm: core: Use U-Boot logging instead of pr_debug()")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>