usb: usb_bam: Prevent closing an un-opened SPS connection

Commit ce5e3f25, "usb: usb_bam: Add support to USB-IPA
BAM2BAM connection", introduced a regression by allowing
closing of a SPS connection even if it was never opened.
This may result in issues like clk_disable APIs getting
called twice resulting in ref_count mismatch.

CRs-fixed: 425510
Change-Id: I9564d6a576b769d725a41290c6b96add6d9f52e2
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>