sh: Kill off the unhandled pvr case in SH-4 CPU probing.

This is superfluous, as the default CPU type and family are already
established by the initial cpuinfo definition. Given that we are still
able to probe for the CPU family even if we are not able to detect the
subtype, it's preferable to let the probing code fill out what it can and
leave the rest.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>