tests/qtest/pflash-cfi02-test: Avoid potential integer overflow

Coverity points out that we calculate a 64-bit value using 32-bit
arithmetic; add the cast to force the multiply to be done as 64-bits.
(The overflow will never happen with the current test data.)

Fixes: Coverity CID 1432320
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Message-id: 20210525134458.6675-5-peter.maydell@linaro.org

tests/qtest/pflash-cfi02-test.c

@@ -406,7 +406,7 @@ static void test_geometry(const void *opaque)
 
     for (int region = 0; region < nb_erase_regions; ++region) {
         for (uint32_t i = 0; i < c->nb_blocs[region]; ++i) {
-            uint64_t byte_addr = i * c->sector_len[region];
+            uint64_t byte_addr = (uint64_t)i * c->sector_len[region];
             g_assert_cmphex(flash_read(c, byte_addr), ==, bank_mask(c));
         }
     }