Fix ValidateRowsPerImage error text.

Bug: None
Change-Id: I4fa934c5cfd5df0b0d18286350640bd1ff9df510
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/20440
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

src/dawn_native/CommandEncoder.cpp

@@ -119,7 +119,7 @@ namespace dawn_native {
 
             if (rowsPerImage % format.blockHeight != 0) {
                 return DAWN_VALIDATION_ERROR(
-                    "rowsPerImage must be a multiple of compressed texture format block width");
+                    "rowsPerImage must be a multiple of compressed texture format block height");
             }
 
             return {};