tcg/optimize: Remove do_default label

tcg/optimize: Remove do_default label

Break the final cleanup clause out of the main switch
statement.  When fully folding an opcode to mov/movi,
use "continue" to process the next opcode, else break
to fall into the final cleanup.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>