objdump.c sign_adjust patch

[Fu, Chao-Ying]

Hi Nick,

  Somehow, the fix for bug 9774 causes a problem for a
mipsisa32r2-sde-elf toolchain.

  When sign_adjust is 0x80000000 and section->vma is 0xffffffff8002000,
addr becomes 0xfffffffe80020000 after "(addr ^ sign_adjust) - sign_adjust".
The while loop at line 1893 (objdump.c) to dump instructions will never exit.
I need to set sign_adjust to 0 to fix this problem.  Thanks a lot!

Regards,
Chao-ying