tests/gem_lut_handle: Quit when we hit ENOSPC

tests/gem_lut_handle: Quit when we hit ENOSPC

I'd been working under the falsehood that we would always generate an
error for an invalid reloc->target_handle before reserving any object.
However, only the execlist is checked up front for validity before
reservation so ENOSPC is a genuine error condition raised by the test.
Fix it so that we stop reporting that limit as a test failure.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65391