powerpc/pseries: Fix clearing of security feature flags

The H_CPU_BEHAV_* flags should be checked for in the 'behaviour' field
of 'struct h_cpu_char_result' -- 'character' is for H_CPU_CHAR_*
flags.

Found by playing around with QEMU's implementation of the hypercall:

  H_CPU_CHAR=0xf000000000000000
  H_CPU_BEHAV=0x0000000000000000

  This clears H_CPU_BEHAV_FAVOUR_SECURITY and H_CPU_BEHAV_L1D_FLUSH_PR
  so pseries_setup_rfi_flush() disables 'rfi_flush'; and it also
  clears H_CPU_CHAR_L1D_THREAD_PRIV flag. So there is no RFI flush
  mitigation at all for cpu_show_meltdown() to report; but currently
  it does:

  Original kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/meltdown
    Mitigation: RFI Flush

  Patched kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/meltdown
    Not affected

  H_CPU_CHAR=0x0000000000000000
  H_CPU_BEHAV=0xf000000000000000

  This sets H_CPU_BEHAV_BNDS_CHK_SPEC_BAR so cpu_show_spectre_v1() should
  report vulnerable; but currently it doesn't:

  Original kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
    Not affected

  Patched kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
    Vulnerable

Brown-paper-bag-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: f636c147 ("powerpc/pseries: Set or clear security feature flags")
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>