arm_tpiu_swo: fix two dead assignments
Clang scan-build complains for two dead assignments:
Value stored to 'retval' is never read
Since the timer callback should not return error, print an error
message if the data cannot be send out. Add a FIXME comment
because in current code there is no string/name to report which
connection has failed.
In command tpiu enable check the returned value and propagate the
error.
Change-Id: I9a89e4c4f7b677e8222b2df09a31b2478ac9ca4f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6588
Tested-by: jenkins