archiver.bbclass: indent fixes

archiver.bbclass: indent fixes

Several fixes:
* It uses mixed tab and whitespace as the indent in one function,
  Fix them to use "4 spaces" as the indent.

* Remove the unwanted blank, for example, more than one blank lines
  appeared together.

* Remove the tail whitespace.

[YOCTO #2619]

(From OE-Core rev: 5eacbcdf306d9e743164a1563559cd24eb5fffe0)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>