staging: most-core: Use bus_find_device_by_name

Use bus_find_device_by_name() helper instead of writing our
own helper.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Christian Gromm <christian.gromm@microchip.com>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>