[rom_ctrl] Use a plus for XOR in the block diagram

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/hw/ip/rom_ctrl/doc/rom_ctrl_blockdiag.svg b/hw/ip/rom_ctrl/doc/rom_ctrl_blockdiag.svg
index 7816059..969c1f5 100644
--- a/hw/ip/rom_ctrl/doc/rom_ctrl_blockdiag.svg
+++ b/hw/ip/rom_ctrl/doc/rom_ctrl_blockdiag.svg
@@ -720,9 +720,9 @@
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-     inkscape:zoom="0.89639071"
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+     inkscape:zoom="1.7927814"
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@@ -820,7 +820,7 @@
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   <g
      id="g914"
-     transform="translate(719.99996,40.000008)"
+     transform="rotate(-45,978.28426,-679.11683)"
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