KVM: s390: fix __insn32_query() inline assembly

The inline assembly constraints of __insn32_query() tell the compiler
that only the first byte of "query" is being written to. Intended was
probably that 32 bytes are written to.

Fix and simplify the code and just use a "memory" clobber.

Fixes: d6681397

 ("KVM: s390: provide query function for instructions returning 32 byte")
Cc: stable@vger.kernel.org # v5.2+
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>