UPSTREAM: drm/i915/dsb: Move the +1 usec adjustment into dsb_wait_usec()

The "wait usec" DSB command doesn't quite seem to able to
guarantee that it always waits at least the specified
amount of usecs. Some of that could be just because it
supposedly just does some kind of dumb timestamp comparison
internally. But I also see cases where two hardware timestamps
sampled on each side of the "wait usec" command come out one
less than expected. So it looks like we always need at least a
+1 to guarantee that we never wait less than specified. Always
apply that adjustment in dsb_wait_usec().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250207223159.14132-2-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
(cherry picked from commit 26b3a8b2)

Bug: 432032023
Test: None
Change-Id: Iadc70ef9035f6dd377161f3f957e045024fa46a3
Signed-off-by: Ap, Kamal <kamal.ap@intel.corp-partner.google.com>