tsm: vte: fix g0-g3 character-set shifting

tsm: vte: fix g0-g3 character-set shifting

A terminal's GL and GR sets can be mapped to 4 different registers g0 to
g3. The g0-g3 registers can be freely set by the application to predefined
or uploaded character-sets.

We implemented GL and GR as separate registers that are set to the current
g0-g3 states when the applications requests a remapping. So subsequent
changes to g0-g3 don't affect GL and GR. Unfortunately, it turns out this
is wrong. GL and GR should point to the g0-g3 registers instead of copying
them.

This commit fixes the GL and GR pointers to point to g0-g3 instead of
pointing to the underlying character sets. This fixes line-drawing
applications like alsamixer, make-menuconfig and other ncurses based
software.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>