power: smb5: Fix initialization error

Function smblib_select_sec_charger_locked will return uninitialized
value of rc in case secondary charger is disabled. Fix by initializing
rc to default value of 0.

Change-Id: I147a6c1927107680922aefd22fbe76e8d0182533
Signed-off-by: Umang Agrawal <uagrawal@codeaurora.org>