ocking of the i2c_clients when in use

Lock the i2c_client pointers and prevent i2c_client removal when
lirc_zilog is perfoming a series of operations that require valid
i2c_client pointers.

Signed-off-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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