aerdrv: Cleanup log output for AER

These changes make cper_print_aer more consistent with aer_print_error
and clean things up by elimiating the use of the prefix variable and
replacing it with dev_printk.

Signed-off-by: Lance Ortiz <lance.ortiz@hp.com>
Acked-by: Boris Petkov <bp@alien8.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>