[lldb] Fix a warning

This patch fixes:

  lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:4843:13:
  error: 225 enumeration values not handled in switch: 'RvvInt8mf8x2',
  'RvvInt8mf8x3', 'RvvInt8mf8x4'... [-Werror,-Wswitch]