drm/radeon: remove set but not used variable 'radeon_connector'

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

drivers/gpu/drm/radeon/radeon_display.c: In function radeon_crtc_scaling_mode_fixup:
drivers/gpu/drm/radeon/radeon_display.c:1685:27: warning: variable radeon_connector set but not used [-Wunused-but-set-variable]

It is not used since commit 377bd8a9 ("drm/radeon:
use a fetch function to get the edid")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>