drm/amd: Drop unnecessary check in amdgpu_connector_add_common_modes()

drm/amd: Drop unnecessary check in amdgpu_connector_add_common_modes()

[Why]
amdgpu_connector_add_common_modes() has a check for the width and height
of common modes being too small, but the array of common_modes[] has fixed
values.  The check is dead code.

[How]
Drop unnecessary check.

Cc: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://lore.kernel.org/r/20250924161624.1975819-3-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>