drm/xe/pf: Fix use-after-free in migration restore

drm/xe/pf: Fix use-after-free in migration restore

When an error is returned from xe_sriov_pf_migration_restore_produce(),
the data pointer is not set to NULL, which can trigger use-after-free
in subsequent .write() calls.
Set the pointer to NULL upon error to fix the problem.

Fixes: 1ed30397c0b92 ("drm/xe/pf: Add support for encap/decap of bitstream to/from packet")
Reported-by: Sebastian Österlund <sebastian.osterlund@intel.com>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7230
Reviewed-by: Shuicheng Lin <shuicheng.lin@intel.com>
Link: https://patch.msgid.link/20260217154118.176902-1-michal.winiarski@intel.com
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>