tv: mixer: Fix build warning due to possible uninitialized usage

tv: mixer: Fix build warning due to possible uninitialized usage

Fix the following build error in exynos' mixer driver:

drivers/media/video/exynos/tv/mixer_drv.c: In function 'mxr_s_stream':
drivers/media/video/exynos/tv/mixer_drv.c:281:9: warning: 'hdmi_sd' may be
used uninitialized in this function [-Wmaybe-uninitialized]
drivers/media/video/exynos/tv/mixer_drv.c:217:22: note: 'hdmi_sd' was
declared here

BUG=chrome-os-partner:9696
TEST=build and boot on SMDK

Change-Id: If22eac90c5a1906aab7c6a7647f4db4b721f5dde
Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Reviewed-on: https://gerrit-int.chromium.org/17828
Reviewed-by: Prashanth Godrehal <prashanth.g@samsung.com>
Commit-Ready: Olof Johansson <olofj@google.com>
Reviewed-by: Olof Johansson <olofj@google.com>
Tested-by: Olof Johansson <olofj@google.com>