drm/i915/selftests: Do not use import_obj uninitialized

Clang warns a couple of times:

drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c:63:6: warning:
variable 'import_obj' is used uninitialized whenever 'if' condition is
true [-Wsometimes-uninitialized]
        if (import != &obj->base) {
            ^~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c:80:22: note:
uninitialized use occurs here
        i915_gem_object_put(import_obj);
                            ^~~~~~~~~~
drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c:63:2: note: remove
the 'if' if its condition is always false
        if (import != &obj->base) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c:38:46: note:
initialize the variable 'import_obj' to silence this warning
        struct drm_i915_gem_object *obj, *import_obj;
                                                    ^
                                                     = NULL

Shuffle the import_obj initialization above these if statements so that
it is not used uninitialized.

Fixes: d7b2cb38 ("drm/i915/gem: Correct the locking and pin pattern for dma-buf (v8)")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210824225427.2065517-2-nathan@kernel.org