This is a minor cleanup to change tui_get_low_disassembly_address to
use TUI_DISASM_WIN, rather than the tui_win_list array. This is more
in line with what the rest of the TUI code does.
gdb/ChangeLog
2020-02-22 Tom Tromey <tom@tromey.com>
* tui/tui-disasm.c (tui_get_low_disassembly_address): Use
TUI_DISASM_WIN, not tui_win_list.