Documentation: drm: Fix tablulation in KMS properties table

Commit 712a0dd9 ("Documentation/drm: Update rotation property")
left an extra 'rowspan' for the row omap, which pushed the following qxl
rows columns out to column 8 and broke the tabulation.
Remove the errant rowspan.

Signed-off-by: Graham Whaley <graham.whaley@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>