[media] em28xx: i2c RC devices: minor code size and memory usage optimization

Set up the i2c_client locally in em28xx_i2c_ir_handle_key().

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>