ANDROID: properly export new symbols with _GPL tag

For new symbols that are exported based on non-upstream patches, the
exports must be _GPL in order to make sure nothing funny is happening
here.

This fixes up 50f0dd43 ("ANDROID: sdcardfs: Enable modular
sdcardfs") to properly export things correctly.

Cc: Daniel Rosenberg <drosen@google.com>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Alistair Strachan <astrachan@google.com>
Reported-by: Karim Yaghmour <karim.yaghmour@opersys.com>
Reported-by: François-Denis Gonthier <francois-denis.gonthier@opersys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I0d663c08d34be74b19c84cdc1d3c7a2b90a029e6