Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/display/dc/bios/bios_parser.c: In function bios_get_board_layout_info:
drivers/gpu/drm/amd/display/dc/bios/bios_parser.c:2743:22: warning: variable bp set but not used [-Wunused-but-set-variable]

It is introduced by commit 1eeedbcc ("drm/amd/display:
get board layout for edid emulation"), but never used,
so remove it.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>