[sw] Correct EXPECT_MASK8 mmio macro

Signed-off-by: Sam Elliott <selliott@lowrisc.org>
diff --git a/sw/device/lib/testing/mock_mmio.h b/sw/device/lib/testing/mock_mmio.h
index f30e247..a55f231 100644
--- a/sw/device/lib/testing/mock_mmio.h
+++ b/sw/device/lib/testing/mock_mmio.h
@@ -394,7 +394,7 @@
  * calls.
  */
 #define EXPECT_MASK8(offset, ...) \
-  EXPECT_MASK32_AT(this->dev(), offset, __VA_ARGS__)
+  EXPECT_MASK8_AT(this->dev(), offset, __VA_ARGS__)
 
 /**
  * Expect an unspecified 32-bit read at the given offset, followed by a write to