drivers: video: tegra: fix compilation error on Google GCC 4.7

drivers/video/tegra/dc/nvhdcp.c: In function 'nvhdcp_downstream_worker':
drivers/video/tegra/dc/nvhdcp.c:826:9: error: 'b_status' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/video/tegra/dc/nvhdcp.c:782:6: note: 'b_status' was declared here
cc1: all warnings being treated as errors