package/libblockdev: fix build with libglib2 >= 2.69

Fix the following build failure raised since bump of libglib2 to version
2.70 in commit 079923d5:

exec.c: In function 'bd_utils_exec_and_report_status_error':
exec.c:239:5: error: 'g_spawn_check_exit_status' is deprecated: Use 'g_spawn_check_wait_status' instead [-Werror=deprecated-declarations]
  239 |     if (!g_spawn_check_exit_status (exit_status, error)) {
      |     ^~

Fixes:
 - http://autobuild.buildroot.org/results/8f9ca895cb07014804130a7ccbcb758b1d519470



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>