s390: Fix fall-through warnings for Clang

Fix the following fallthrough warnings:

drivers/s390/net/ctcm_fsms.c:1457:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
drivers/s390/net/qeth_l3_main.c:437:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
drivers/s390/char/tape_char.c:374:4: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
arch/s390/kernel/uprobes.c:129:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]

Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>