core: Fix results returned by gpgme_data_* functions

src/debug.h (TRACE_SYSRES_OFF_T, _trace_sysres_off_t,
TRACE_SYSRES_SSIZE_T, _trace_sysres_ssize_t): New.
src/data.c (gpgme_data_read, gpgme_data_write, gpgme_data_seek): Use

appropriate new tracing macros instead of casting the results to int.

This change adds tracing macros for results of system functions of
type off_t and ssize_t.

• GnuPG-bug-id: T5481