Fix incompatible pointer type warning

Fix incompatible pointer type warning

[   54s] /home/abuild/rpmbuild/BUILD/org.tizen.settings-tv-ref-0.1/src
         /view_maincatalog.c: In function '_draw_subitems':
[   54s] /home/abuild/rpmbuild/BUILD/org.tizen.settings-tv-ref-0.1/src
         /view_maincatalog.c:1181:45: warning: passing argument 2 of
         'provider_get_passcode' from incompatible pointer type
[   54s] && (provider_get_passcode(KEY_PASSCODE, &passcode) == -1)) {
[   54s]                                              ^
[   54s] In file included from /home/abuild/rpmbuild/BUILD/
         org.tizen.settings-tv-ref-0.1/src/view_maincatalog.c:28:0:
[   54s] /home/abuild/rpmbuild/BUILD/org.tizen.settings-tv-ref-0.1/
         include/settings_provider.h:28:5: note: expected 'char **'
         but argument is of type 'const char **'
[   54s]  int provider_get_passcode(const char *key, char **val);
[   54s]      ^

Change-Id: I4926ee81a6f19504ea8b6b5721fbf5d827bcaf0a