module.h: Annotate mod_kallsyms with __rcu

This patch fixes the following sparse errors:

kernel/module.c:3623:9: error: incompatible types in comparison expression
kernel/module.c:4060:41: error: incompatible types in comparison expression
kernel/module.c:4203:28: error: incompatible types in comparison expression
kernel/module.c:4225:41: error: incompatible types in comparison expression

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>