USB: u_data_ipa: Fix pm_runtime usage count in case of error

If disconnect happens before connect_work start executing, then
there is a chance that connect_work returns with port_usb NULL.
Due to this, port->is_connected will be NULL and disconnect_work
returns with this check, but not decremented pm_usage count, which
is incremented before scheduling connect_work in ipa_data_connect.
Hence fix this by decrementing pm_usage count in connect_work if
port_usb is NULL.

Change-Id: Ic60f2addcf07375429e0858d3c7a376a35132750
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>