vfs: end message printed by sys_panic() with new line

Looks like the serial console doesn't display anything
until new line character is received.

Looks like only when '\n' is written to the serial console
QEMU displays the line.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>