perf probe: Fix uninitialized variable

perf probe: Fix uninitialized variable

Since the linked fixes: commit, err is returned uninitialized due to the
removal of "return 0". Initialize err to fix it.

This fixes the following intermittent test failure on release builds:

 $ perf test "testsuite_probe"
 ...
 -- [ FAIL ] -- perf_probe :: test_invalid_options :: mutually exclusive options :: -L foo -V bar (output regexp parsing)
 Regexp not found: \"Error: switch .+ cannot be used with switch .+\"
 ...

Fixes: 080e47b2a237 ("perf probe: Introduce quotation marks support")
Tested-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20241211085525.519458-2-james.clark@linaro.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>