s3/registry: fix various 'cast between incompatible function' warnings

s3/registry: fix various 'cast between incompatible function' warnings

[3395/3524] Compiling source3/registry/reg_import.c
../../source3/registry/reg_import.c: In function ‘reg_import_adapter’:
../../source3/registry/reg_import.c:237:16: error: cast between incompatible function types from ‘int (*)(void *)’ to ‘WERROR (*)(void *, void *, const char *, void **)’ {aka ‘struct <anonymous> (*)(void *, void *, const char *, void **)’} [-Werror=cast-function-type]
   cb.openkey = (reg_import_callback_openkey_t)&nop;
                ^
../../source3/registry/reg_import.c:240:17: error: cast between incompatible function types from ‘int (*)(void *)’ to ‘WERROR (*)(void *, void *)’ {aka ‘struct <anonymous> (*)(void *, void *)’} [-Werror=cast-function-type]
   cb.closekey = (reg_import_callback_closekey_t)&nop;
                 ^
../../source3/registry/reg_import.c:243:18: error: cast between incompatible function types from ‘int (*)(void *)’ to ‘WERROR (*)(void *, void *, const char *, void **, _Bool *)’ {aka ‘struct <anonymous> (*)(void *, void *, const char *, void **, _Bool *)’} [-Werror=cast-function-type]
   cb.createkey = (reg_import_callback_createkey_t)&nop;
                  ^
../../source3/registry/reg_import.c:246:18: error: cast between incompatible function types from ‘int (*)(void *)’ to ‘WERROR (*)(void *, void *, const char *)’ {aka ‘struct <anonymous> (*)(void *, void *, const char *)’} [-Werror=cast-function-type]
   cb.deletekey = (reg_import_callback_deletekey_t)&nop;
                  ^
../../source3/registry/reg_import.c:249:18: error: cast between incompatible function types from ‘int (*)(void *)’ to ‘WERROR (*)(void *, void *, const char *)’ {aka ‘struct <anonymous> (*)(void *, void *, const char *)’} [-Werror=cast-function-type]
   cb.deleteval = (reg_import_callback_deleteval_t)&nop;

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>