ASoC: core: Don't probe the component which is dummy

Dummy dai can be used by multiple sound card. But it only belong to one
card's dapm list. If another card use it, there will be dapm_assert_locked
warning.

[   20.015782] WARNING: CPU: 1 PID: 661 at sound/soc/soc-dapm.c:124 dapm_assert_locked.isra.36+0x4c/0x58()
[   20.025249] Modules linked in:
[   20.028349] CPU: 1 PID: 661 Comm: aplay Not tainted 4.1.0-rc6-next-20150605-00004-gaee05d8-dirty #92
[   20.037528] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[   20.044110] Backtrace:
[   20.046614] [<80012e00>] (dump_backtrace) from [<80012fa0>] (show_stack+0x18/0x1c)
[   20.054229]  r6:809e8060 r5:00000000 r4:00000000 r3:00000000
[   20.060002] [<80012f88>] (show_stack) from [<807a0f74>] (dump_stack+0x80/0x9c)
[   20.067293] [<807a0ef4>] (dump_stack) from [<8002b144>] (warn_slowpath_common+0x7c/0xb4)
[   20.075427]  r5:0000007c r4:00000000
[   20.079065] [<8002b0c8>] (warn_slowpath_common) from [<8002b1a0>] (warn_slowpath_null+0x24/0x2c)
[   20.087898]  r8:00000001 r7:88007c28 r6:ed94a680 r5:809e83e4 r4:ed83d6c0
[   20.094747] [<8002b17c>] (warn_slowpath_null) from [<8058403c>] (dapm_assert_locked.isra.36+0x4c/0x58)
[   20.104101] [<80583ff0>] (dapm_assert_locked.isra.36) from [<805842ec>] (dapm_mark_dirty+0x64/0xa4)
[   20.113165] [<80584288>] (dapm_mark_dirty) from [<805853a8>] (soc_dapm_dai_stream_event.isra.42+0x30/0xc8)
[   20.122863]  r8:ed9b5dbc r7:00000000 r6:00000001 r5:00000001 r4:ed83d6c0
[   20.129706] [<80585378>] (soc_dapm_dai_stream_event.isra.42) from [<80587e28>] (snd_soc_dapm_stream_event+0x78/0xa0)
[   20.140264]  r5:ee2ee62c r4:00000001
[   20.143918] [<80587db0>] (snd_soc_dapm_stream_event) from [<8058957c>] (soc_pcm_prepare+0x138/0x21c)
[   20.153058]  r8:ed8d9480 r7:00000000 r6:ed9b0e00 r5:00000001 r4:ee2ee62c r3:00000000
...

This patch is to not probe the dummy component in soc_probe_component. Then
there is no widget created for dummy DAI, and also don't need to check the
dummy dai in dapm_connect_dai_link_widgets().

Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>