ASN.1: add module description

ASN.1: add module description

This is needed to avoid a build warning:

WARNING: modpost: missing MODULE_DESCRIPTION() in lib/asn1_decoder.o

Link: https://lkml.kernel.org/r/20250324173242.1501003-2-arnd@kernel.org
Fixes: 6c6c1fc09de3 ("modpost: require a MODULE_DESCRIPTION()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Stehen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>