[S390] virtio console: fix section mismatch warning.

Fix these two false positive warnings:

WARNING: vmlinux.o(.text+0x2e1cc4): Section mismatch in reference from the function s390_virtio_console_init() to the function .init.text:early_put_chars()
The function s390_virtio_console_init() references
the function __init early_put_chars().
This is often because s390_virtio_console_init lacks a __init
annotation or the annotation of early_put_chars is wrong.

WARNING: vmlinux.o(.text+0x2e1cd0): Section mismatch in reference from the function s390_virtio_console_init() to the function .init.text:virtio_cons_early_init()
The function s390_virtio_console_init() references
the function __init virtio_cons_early_init().
This is often because s390_virtio_console_init lacks a __init
annotation or the annotation of virtio_cons_early_init is wrong.

Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>