The device_error() takes a printf style string, so update the prototype
accordingly. The message should be const and it should use an attribute.
This fixes gcc warnings like:
sim-core.c: In function 'sim_core_map_attach':
sim-core.c:200: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
sim-core.c:237: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
sim-core.c: In function 'sim_core_attach':
sim-core.c:304: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
sim-core.c:314: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
sim-core.c:335: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
sim-core.c:348: warning: passing argument 2 of 'device_error' discards qualifiers from pointer target type
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