tests: drivers: flash: Improve compatibility with 64-bit platforms

[tpambor]

Change variables in test_cb_data_type from uint32_t to size_t to match the return type of flash_get_page_count() and adjust format specifiers accordingly. This resolves warnings when compiling for 64-bit platforms.

/home/user/west_workspace/zephyr/tests/drivers/flash/common/src/main.c: In function 'flash_driver_test_flash_page_layout':
/home/user/west_workspace/zephyr/tests/drivers/flash/common/src/main.c:416:22: error: format '%d' expects argument of type 'int', but argument 7 has type 'size_t' {aka 'long unsigned int'} [-Werror=format=]
  416 |                      "page_count = %d not equal to pages counted with cb = %d", page_count,
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ~~~~~~~~~~
      |                                                                                 |
      |                                                                                 size_t {aka long unsigned int}

Part of #96968

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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