drm/amd/display: Remove unreachable check

[WHY]
Coverity analysis flagged this code as DEADCODE
since the condition and return in the outer loop
are never reached.

All operations with the 'dwb_pipe' variable happen
in the inner loop, that already contains the same
check with the 'MAX_DWB_PIPES'. The later
check condition cannot occur before the check
condition in the inner loop, thus the later
condition is unreacable.

[HOW]
Remove the unreachable condition.

Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Ivan Lipski <ivlipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>