devOmsCom.cc is not completely device independent

[kmpeters]

@hjunkes reported the following in epics-modules/motor#179:

In devOmsCom.cc the hard-coded driver table of the oms58 is used.
I don't understand the construct, but shouldn't e.g. when using a MAXv card,
the driver table of that card (MAVv_access) be accessed?

Line 247:
if ((command == PRIMITIVE) && (mr->init != NULL) &&
(strlen(mr->init) != 0))
{
extern struct driver_table oms58_access;
/* Test for a "device directive" in the Initialization string. */
if ((mr->init[0] == '@') && (trans->tabptr == &oms58_access))
{
char *end = strrchr(&mr->init[1], '@');
if (end != NULL)
{