net: smc911x: Drop weak alias from 32bit accessors

These accessors are not overridden by any board, and even if they were,
this is something which should be handled via DM now, so remove the
weak alias option. Moreover, drop the inline keyword, as the compiler
can decide better.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>