Documentation: ubsan: drop "the" from article title

Drop "the" from the title of the documentation article for UBSAN, as it is
redundant.

Also add SPDX-License-Identifier for ubsan.rst.

Link: https://lkml.kernel.org/r/5fb11a4743eea9d9232a5284dea0716589088fec.1698161845.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/dev-tools/ubsan.rst

-The Undefined Behavior Sanitizer - UBSAN
-========================================
+.. SPDX-License-Identifier: GPL-2.0
+
+Undefined Behavior Sanitizer - UBSAN
+====================================
 
 UBSAN is a runtime undefined behaviour checker.