Fix endian test for big-endian hosts

The uint16_t cast truncated the magic value to 0x00000304, making the
first byte 0 (eByteOrderInvalid) on big endian hosts.

Reported by Justin Hibbits.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@213861 91177308-0d34-0410-b5e6-96231b3b80d8