tracing/tools: Fix incorrcet short option in usage text for --threads

The help message incorrectly listed '-t' as the short option for
--threads, but the actual getopt_long configuration uses '-e'.
This mismatch can confuse users and lead to incorrect command-line
usage. This patch updates the usage string to correctly show:
"-e, --threads NRTHR"
to match the implementation.

Note: checkpatch.pl reports a false-positive spelling warning on
'Run', which is intentional.

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Zhang Chujun <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

tools/tracing/latency/latency-collector.c

···
 "-n, --notrace\t\tIf latency is detected, do not print out the content of\n"
 "\t\t\tthe trace file to standard output\n\n"
 
-"-t, --threads NRTHR\tRun NRTHR threads for printing. Default is %d.\n\n"
+"-e, --threads NRTHR\tRun NRTHR threads for printing. Default is %d.\n\n"
 
 "-r, --random\t\tArbitrarily sleep a certain amount of time, default\n"
 "\t\t\t%ld ms, before reading the trace file. The\n"