i965: Extend the negative 32-bit deltas to 64-bits

i965: Extend the negative 32-bit deltas to 64-bits

Gen8+ use 48-bit address relocations so need to extend the sign
to 64-bit return value. Without it we have higher bits zeroed
and missing the negavive values.
Haswell and older use 32-bit deltas so are unaffected by this issue.

v2:
  used int32_t fucntion parameter instead of explicit type conversion.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101408
Signed-off-by: Sergii Romantsov <sergii.romantsov@globallogic.com>
Tested-by: Andriy Khulap <andriy.khulap@globallogic.com>
Tested-by: Stuart Young <cefiar@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: "18.0 17.3" <mesa-stable@lists.freedesktop.org>