i965: Fix check for negative pitch in can_do_fast_copy_blit().

i965: Fix check for negative pitch in can_do_fast_copy_blit().

At this point, the pitch is in bytes.  We haven't yet divided the pitch
by 4 for tiled surfaces, so abs(pitch) may be larger than 32K.  This
means the bit 15 trick won't work.

The caller now has signed integers anyway, so just pass those through
and do the obvious check.

Cc: "17.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>