powerpc/pseries/hvconsole: Fix dropped console output

Return -EAGAIN when we get H_BUSY back from the hypervisor. This
makes the hvc console driver retry, avoiding dropped printks.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: <stable@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/hvconsole.c

@@ -73,7 +73,7 @@ int hvc_put_chars(uint32_t vtermno, const char *buf, int count)
 	if (ret == H_SUCCESS)
 		return count;
 	if (ret == H_BUSY)
-		return 0;
+		return -EAGAIN;
 	return -EIO;
 }