hw/intc/arm_gicv3: Fix write of ICH_VMCR_EL2.{VBPR0, VBPR1}

hw/intc/arm_gicv3: Fix write of ICH_VMCR_EL2.{VBPR0, VBPR1}

In ich_vmcr_write() we enforce "writes of BPR fields to less than
their minimum sets them to the minimum" by doing a "read vbpr and
write it back" operation.  A typo here meant that we weren't handling
writes to these fields correctly, because we were reading from VBPR0
but writing to VBPR1.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20190520162809[email protected]