Accesses with _nucleus prefix are not available when building user
emulators:
  CC    sparc64-linux-user/op_helper.o
cc1: warnings being treated as errors
/src/qemu/target-sparc/op_helper.c: In function 'helper_ldda_asi':
/src/qemu/target-sparc/op_helper.c:3063: error: implicit declaration of function 'ldq_nucleus'

Avoid making such accesses. Fixes breakage by 54a3c0f0.
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>