ASoC: msm: q6dspv2: add check for APR handle before using APR

APR registration must be suceessful and a non-NULL handle must be
returned from APR driver before the servicec can be used for
communicating. Add a check in q6core driver to see if the APR
registration is done successfully before sending any APR packet.

CRs-fixed: 2022490
Change-Id: I88b09f3e1f58b0147b81ee734f87906c7ef09167
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>