-Wconstant-conversion in drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c

[nathanchance]

After llvm/llvm-project@a5ef934:

drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:224:18: warning: implicit conversion from 'int' to 's8' (aka 'signed char') changes value from 128 to -128 [-Wconstant-conversion]
  224 |         {0, 0, 0, 0, 0, 128},
      |         ~               ^~~