AT91 MMC 5 : Minor cleanups

A number of small cleanups to the AT91RM9200 MMC driver:
 - fix warnings generated by pr_debug().
 - prepend "AT91 MMC:" to printk() messages.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>