hal: msm8916: Fix for vndk compilation errors

There are few Implicit declaration compilation errors for
not including required header files for system functions call.
Added required header file to fix the compilation errors.

CRs-Fixed: 2258838
Change-Id: Iffd8a3c00a2a1ad063e10c0ebf3ce9e88e3edea0
diff --git a/hal/msm8916/platform.c b/hal/msm8916/platform.c
index d65c389..6a00883 100644
--- a/hal/msm8916/platform.c
+++ b/hal/msm8916/platform.c
@@ -30,6 +30,7 @@
 #include <cutils/str_parms.h>
 #include <audio_hw.h>
 #include <platform_api.h>
+#include <unistd.h>
 #include "platform.h"
 #include "audio_extn.h"
 #include "acdb.h"