coresight: etm3x: making error message unambiguous

By adding the function name at the beginning of the error
message there is no doubt as to where the failing condition
occurred.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>