drm/radeon: Fix encoder->possible_clones

In the Linux kernel, the following vulnerability has been resolved:

drm/radeon: Fix encoder->possible_clones

Include the encoder itself in its possible_clones bitmask.

In the past nothing validated that drivers were populating

possible_clones correctly, but that changed in commit

74d2aacbe840 ("drm: Validate encoder->possible_clones").

Looks like radeon never got the memo and is still not

following the rules 100% correctly.

This results in some warnings during driver initialization:

Bogus possible_clones: [ENCODER:46:TV-46] possible_clones=0x4 (full encoder mask=0x7)

WARNING: CPU: 0 PID: 170 at drivers/gpu/drm/drm_mode_config.c:615 drm_mode_config_validate+0x113/0x39c

...

(cherry picked from commit 3b6e7d40649c0d75572039aff9d0911864c689db)