Using jniThrowErrnoException in android_os_SharedMemory

Since libnativehelper now has an implementation of jniThrowErrnoException,
this method is now used when a system error occurs to avoid code
duplication.

Bug: 180958753
Test: m
Change-Id: I65d9b58d2cb2d94af97f77a15264137b0c7d0462