Look for both fdtaddr and fdt_addr env var names. Grepping the u-boot

Look for both fdtaddr and fdt_addr env var names.  Grepping the u-boot
source shows that board vendors seem to be about evenly split on this.

This commit is a trivial change to note that while the previous change
was supposed to be whitespace only, this functional change also crept in.
The added lines were:

  /* Board vendors use both fdtaddr and fdt_addr names.  Grrrr. */

  if (s == NULL)
	s = ub_env_get("fdt_addr");