The tracing_set_trace_write() function just removes the trailing whitespace
from the user supplied tracer name, but the leading whitespace should also
be removed.

In addition, if the user supplied tracer name contains only a few
whitespace characters, the first one will not be removed using the current
method, which results it a single whitespace character left in the buf.

To fix all of these issues, we use strim() to correctly remove both the
leading and trailing whitespace.

Link: https://lkml.kernel.org/r/20220121095623.1826679-1-ytcoode@gmail.comSigned-off-by: Yuntao Wang <ytcoode@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>