tracing: Remove size restriction on tracing_log_err cmd strings

Currently, tracing_log_err.cmd strings are restricted to a length of
MAX_FILTER_STR_VAL (256), which is too short for some commands already
seen in the wild (with cmd strings longer than that showing up
truncated).

Remove the restriction so that no command string is ever truncated.

Link: https://lkml.kernel.org/r/ca965f23256b350ebd94b3dc1a319f28e8267f5f.1643319703.git.zanussi@kernel.org

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>