intel/compiler: invert the logic of lower_integer_multiplication()

intel/compiler: invert the logic of lower_integer_multiplication()

Invert the logic of how progress is handled: remove the continue
statements and mark progress inside the places where it actually
happens.

We're going to add a new lowering that also looks for BRW_OPCODE_MUL,
so inverting the logic here makes the resulting code much easier to
follow.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>