Revert "ALSA: pcm: Check for null pointer of pointer substream before dereferencing it"

This reverts commit b2421a19 which is
commit 011b559b upstream.

It breaks the Android abi.  If it is required in the future, it can
come back in an abi-safe way.

Bug: 161946584
Change-Id: I4278870e1e9f98ba86e52d588d1b208a6b3255ba
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>