drm/amd/display: Fix a potential buffer overflow in 'dp_dsc_clock_en_read()'

Tell snprintf() to store at most 10 bytes in the output buffer
instead of 30.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_debugfs.c:1508 dp_dsc_clock_en_read() error: snprintf() is printing too much 30 vs 10

Fixes: c06e09b7

 ("drm/amd/display: Add DSC parameters logging to debugfs")
Cc: Alex Hung <alex.hung@amd.com>
Cc: Qingqing Zhuo <qingqing.zhuo@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>