KVM: PPC: Book3S HV: Fix thinko in try_lock_hpte()

This fixes an error in the inline asm in try_lock_hpte() where we
were erroneously using a register number as an immediate operand.
The bug only affects an error path, and in fact the code will still
work as long as the compiler chooses some register other than r0
for the "bits" variable.  Nevertheless it should still be fixed.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>