The R8A7791 manual sometimes calls the signal MLB_CLK and sometimes MLB_CK; the
latter can only be encountered in the PFC section and is probably just a typo
(this signal is always called MLB_CLK in the R8A7790 manual). Fix occurences
of MLB_CK throughout the R8A7791 PFC driver.
Based on original patch by Andrey Gusakov <andrey.gusakov@cogentembedded.com>.