rtla: Don't overwrite existing directory mode

The mode on /usr/bin is often 555 these days,
but make install on rtla overwrites this with 755

Fix this by preserving the current directory if it exists.

Link: https://lkml.kernel.org/r/8c294a6961080a1970fd8b73f7bcf1e3984579e2.1651247710.git.bristot@kernel.org
Link: https://lore.kernel.org/r/20220402043939.6962-1-jkacur@redhat.com

Cc: Daniel Bristot de Oliveria <bristot@redhat.com>
Fixes: 79ce8f43

 ("rtla: Real-Time Linux Analysis tool")
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: John Kacur <jkacur@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>