mlxsw: core_env: Convert 'module_info_lock' to a mutex

After the previous patch, the lock is always taken in process context so
it can be converted to a mutex. It is needed for future changes where we
will need to be able to sleep when holding the lock.

Convert the lock to a mutex.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>