firmware-utils: seama.h: replace LGPL-2.1-or-later boilerplate with SPDX

firmware-utils: seama.h: replace LGPL-2.1-or-later boilerplate with SPDX

This was missed because scancode license scanner was confused by a
slightly different than expected license text (96,75% license score).

License text included "file" instead of "library" in the main part of
the licensing info. It also used "The GNU C Library" instead of the
standard "This library" in 2nd and 3rd paragraphs.

The first paragraph clearly mentions LGPL-2.1-or-later and the use of
"file" instead of "library" should not affect licensing.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>