KVM: PPC: Fix vmx/vsx mixup in mmio emulation

The MMIO emulation code for vector instructions is duplicated between
VSX and VMX. When emulating VMX we should check the VMX copy size
instead of the VSX one.

Fixes: acc9eb93

 ("KVM: PPC: Reimplement LOAD_VMX/STORE_VMX instruction ...")
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220125215655.1026224-3-farosas@linux.ibm.com