devtools: fix symbols check

devtools: fix symbols check

In some environments, the check of local symbols catch-all
was failing. Note: this script is called during the build.

The reason is that grep returns an error if nothing is found.
The option -e of the shell script makes this error fatal.
It is not always fatal because the grep is in a command substitution.

Fixes: b403498e1422 ("build: hide local symbols in shared libraries")
Reported-by: Usama Arif <usama.arif@bytedance.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>