Revert "relayfs: abolish prev_padding"

JIRA: https://issues.redhat.com/browse/RHEL-113577
Upstream Status: RHEL only

This reverts commit 2489e95.

This commit was backported automatically as part of the DRM backport.

In this tree the "subbuf_start" callback needs the last "size_t"
argument, restore it.

NOTE: This commit does not compile due to missing RHEL-specific fix-ups,
which are split out into separate Git commits following this one.

If git bisect selected this commit, run "git bisect skip" and try again.
Repeat this until it selects a commit which compiles.

Signed-off-by: José Expósito <jexposit@redhat.com>

Author: jexposit

drivers/gpu/drm/i915/gt/uc/intel_guc_log.c

@@ -220,7 +220,8 @@ static int guc_action_control_log(struct intel_guc *guc, bool enable,
  */
 static int subbuf_start_callback(struct rchan_buf *buf,
 				 void *subbuf,
-				 void *prev_subbuf)
+				 void *prev_subbuf,
+				 size_t prev_padding)
 {
 	/*
 	 * Use no-overwrite mode by default, where relay will stop accepting