MIPS: OCTEON: cvmx-gmxx-defs.h: use default register value return whe…

…n possible

If we are about to return the same register address that would
be the default anyway, fallback to default return instead of adding
a case label.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21200/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org