V4L/DVB (9518): radio-mr800: remove warn, info and err messages

Patch removes warn(), err() and info() statements in
drivers/media/radio/radio-mr800.c, and place dev_warn, dev_info in right
places.
Printk changed on pr_info and pr_err macro. Also new macro
amradio_dev_warn defined. Name in usb driver struct changed on
MR800_DRIVER_NAME.

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Signed-off-by: Alexey Klimov <klimov.linux@gmail.com>
Acked-by: David Ellingsworth <david@identd.dyndns.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>