pinctrl: renesas: checker: Prefix common checker output

Add a "sh_pfc: " prefix to common checker output that is not yet
prefixed by a subdriver-specific prefix ("<SoC-part-number>_pfc: "), for
easier grepping.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/9cf1dc9f895dc5fa74125dabddfe46fecf438b4f.1633615652.git.geert+renesas@glider.be