drm/amd/display: Remove unused NumberOfStates variable

drm/amd/display: Remove unused NumberOfStates variable

Remove the unused unsigned int NumberOfStates from the file, which was
declared but never hooked up.

This was pointed by clang with the following warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/display_mode_vba_32.c:33:27:
warning: unused variable 'NumberOfStates' [-Wunused-const-variable]
static const unsigned int NumberOfStates = DC__VOLTAGE_STATES;
                          ^
1 warning generated.

Reviewed-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>