drm/bridge: analogix: Remove unreachable code from analogic_dp_core.c

This patch removes an unreachable code found by the SVACE static
analysis:

UNREACHABLE_CODE: This statement in the source code might be unreachable
during program execution.
[unreachable] unreachable at drivers/gpu/drm/bridge/analogix/analogix_dp_core.c:787
retval != 0 is always false because at this program point the variable retval
is always equal to 0 at drivers/gpu/drm/bridge/analogix/analogix_dp_core.c:786

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20171212112037.13107-1-s.nawrocki@samsung.com