drm/xe/exec: Fix minor bug related to xe_sync_entry_cleanup

Increment num_syncs after xe_sync_entry_parse() is successful to ensure
the xe_sync_entry_cleanup() logic under "err_syncs" label works correctly.

v2: Use the same pattern as that in xe_vm.c (Matt Brost)

Fixes: dd08ebf6 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240711211203.3728180-1-ashutosh.dixit@intel.com