s390/disassembler: add missing end marker for e7 table

The e7 opcode table does not have an end marker. Hence when trying to
find an unknown e7 instruction the code will access memory behind the
table until it finds something that matches the opcode, or the kernel
crashes, whatever comes first.

This affects not only the in-kernel disassembler but also uprobes and
kprobes which refuse to set a probe on unknown instructions, and
therefore search the opcode tables to figure out if instructions are
known or not.

Cc: <stable@vger.kernel.org> # v3.18+
Fixes: 3585cb02 ("s390/disassembler: add vector instructions")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/dis.c

@@ -1548,6 +1548,7 @@ static struct s390_insn opcode_e7[] = {
 	{ "vfsq", 0xce, INSTR_VRR_VV000MM },
 	{ "vfs", 0xe2, INSTR_VRR_VVV00MM },
 	{ "vftci", 0x4a, INSTR_VRI_VVIMM },
+	{ "", 0, INSTR_INVALID }
 };
 
 static struct s390_insn opcode_eb[] = {