alsa_sound: Initialize the mPfdProxy in constructor

The uninitialised variable of the proxy parameter PfdProxy in the
ALSADevice constructor is initialized to avoid unnecessary call to

(cherry picked from commit 6d812e2cba18aba1c40159b5e5194d225534235a)

sys_close::lib_close without the proxy session enabled.
CRs-Fixed: 428656

Change-Id: I6ab4f02af3aa67efdf90e61a04c7824df143c35e