qcom: qpnp-fg-gen4: Continue fg_gen4_probe() when !DEBUG_FS

fg_gen4_probe() should not be dependent on DEBUG_FS
API's returning success. Continue device probe,
when DEBUG_FS is disabled.

Change-Id: Ibb01e00d4f6cc7982701e8dd2ac2cd51148a9aea
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Rahul Shahare <rshaha@codeaurora.org>