mfd: sm501: Remove unused sm501_find_clock

sm501_find_clock() was added in 2007 as part of
commit b6d6454f ("[PATCH] mfd: SM501 core driver")
but hasn't been used.

Remove it.

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Link: https://lore.kernel.org/r/20250509173521.49596-1-linux@treblig.org


Signed-off-by: Lee Jones <lee@kernel.org>