st3m_gfx: fix initial mode set
This makes initial call to st3m_gfx_set_mode(st3m_gfx_default) do something, doesn't matter for the current configured default mode, but is neccesary in 8bpp modes.
This makes initial call to st3m_gfx_set_mode(st3m_gfx_default) do something, doesn't matter for the current configured default mode, but is neccesary in 8bpp modes.