tests/boot-sector: Fix the bad s390x assembler code

tests/boot-sector: Fix the bad s390x assembler code

There are currently two bugs in s390x_code[]: First, the initial jump
uses the wrong offset, so it was jumping to 0x10014 instead of 0x10010.
Second, LHI only loads the lower 32-bit of the register.

Everything worked fine as long as the s390-ccw bios code was jumping
here with r3 containing zeroes in the uppermost 48 bit - which just
happened to be the case so far by accident. But we can not rely on this
fact, and indeed one of the recent suggested patches to jump2ipl.c cause
the newer GCCs to put different values into r3. In that case the code
from s390x_code[] crashes very ungracefully.

Thus let's make sure to jump to the right instruction, and use LGHI
instead of LHI to make sure that we always zero out the upper bits
of the register.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20191217150642.27946-1-thuth@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>