bus: mvebu-mbus: Use pr_fmt

In order to clean message printing, we replace pr_info with pr_fmt.
This is purely cosmetic change, with the sole purpose of making
the code a bit more readable.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>