arm: mach-k3: am625_init: Convert rtc_erratumi2327_init to static

arm: mach-k3: am625_init: Convert rtc_erratumi2327_init to static

The erratum is called locally, make it static, drop the #ifdeffery since
it will only be called in R5 build and mark it potentially unused to
stop compiler screaming at us.

While at this, drop the redundant return for a void function.

Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Nishanth Menon <nm@ti.com>