powerpc/powernv: Rate limit opal-elog read failure message

Sometimes we can't read an error log from OPAL, and we print an error
message accordingly. But the OPAL userspace tools seem to like retrying a
lot, in which case we flood the kernel log with a lot of messages.

Change pr_err() to pr_err_ratelimited() to help with this.
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201211021140.28402-1-ajd@linux.ibm.com

arch/powerpc/platforms/powernv/opal-elog.c

@@ -171,8 +171,8 @@ static ssize_t raw_attr_read(struct file *filep, struct kobject *kobj,
 		opal_rc = opal_read_elog(__pa(elog->buffer),
 					 elog->size, elog->id);
 		if (opal_rc != OPAL_SUCCESS) {
-			pr_err("ELOG: log read failed for log-id=%llx\n",
-			       elog->id);
+			pr_err_ratelimited("ELOG: log read failed for log-id=%llx\n",
+					   elog->id);
 			kfree(elog->buffer);
 			elog->buffer = NULL;
 			return -EIO;