drm/xe/xe_sriov_packet: Return int from pf_descriptor_init

drm/xe/xe_sriov_packet: Return int from pf_descriptor_init

pf_descriptor_init currently returns a size_t, which is an unsigned
integer data type.  This conflicts with it returning a negative errno
value on failure.

Make it return an int instead.  This mirrors how pf_trailer_init is used
later.

Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Alex Zuo <alex.zuo@intel.com>
Link: https://patch.msgid.link/20251117190114.69953-2-jonathan.cavitt@intel.com
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>