drm/amd/display: Initialize 'wait_time_microsec' variable in link_dp_training_dpia.c

wait_time_microsec = max(wait_time_microsec, (uint32_t)
DPIA_CLK_SYNC_DELAY);

Above line is trying to assign the maximum value between
'wait_time_microsec' and 'DPIA_CLK_SYNC_DELAY' to wait_time_microsec.
However, 'wait_time_microsec' has not been assigned a value before this
line, initialize 'wait_time_microsec' at the point of declaration.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_dpia.c:697 dpia_training_eq_non_transparent() error: uninitialized symbol 'wait_time_microsec'.

Fixes: 630168a9 ("drm/amd/display: move dp link training logic to link_dp_training")
Cc: Wenjing Liu <wenjing.liu@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>