soc: qcom: bgrsb: check BG response

RSB driver sends configure command to Blackghost
and should wait before reading the response from BG.
Fixes issue where RSB driver sends enable command
even though BG is not configured.

Change-Id: I5ae816d07762e3e26d16923b5767ba2ae9120781
Signed-off-by: Protik Biswas <protbisw@codeaurora.org>