KVM: PPC: Book3S HV: Fix stack frame regs marker

The hard-coded marker is out of date now, fix it using the nice define.

Fixes: 17773afd

 ("powerpc/64: use 32-bit immediate for STACK_FRAME_REGS_MARKER")
Reported-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221006143345.129077-1-npiggin@gmail.com