sh: pfc: Fix up BUG() triggered by gpiolib debugfs lookups.

sh: pfc: Fix up BUG() triggered by gpiolib debugfs lookups.

The gpiolib debugfs entry takes a hammer approach and iterates over all
of the potential GPIOs, regardless of their type. The SH PFC code on the
other hand contains a variable mismash of input/output/function types
spread out sparsely, leading to situations where the debug code can
trigger an out of range enum for the type. Since we already have an error
path for out of range enums, we can just hand that up to the higher level
instead of the current BUG() behaviour.

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