KEYS: trusted: add missing MODULE_DESCRIPTION()

kbuild reports:

WARNING: modpost: missing MODULE_DESCRIPTION() in security/keys/trusted-keys/trusted.o

Add the missing MODULE_DESCRIPTION() macro invocation.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>