drm/vmwgfx: clamp dirty-page range with min, not max

vmw_bo_dirty_transfer_to_res() and vmw_bo_dirty_clear() compute the
intersection of a resource's page range with the BO's tracked dirty
range, but clamp res_end against dirty->end with max() instead of
min().  When dirty->end exceeds the resource end, the loop walks past
the resource's pages, calls vmw_resource_dirty_update() for ranges
owned by other resources sharing the same backing MOB and clears
their pending dirty bits via bitmap_clear().  The result is silent
loss of writeback for unrelated resources whenever two resources
share a MOB.

Use min() in both functions so the loop is bounded to the
intersection of the resource and dirty ranges.

Fixes: b7468b15d271 ("drm/vmwgfx: Implement an infrastructure for write-coherent resources")
Fixes: 965544150d1c ("drm/vmwgfx: Refactor cursor handling")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Ian Forbes <ian.forbes@broadcom.com>
Link: https://patch.msgid.link/20260505222728.519626-4-zack.rusin@broadcom.com

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