ANDROID: SoC: core: fix export symbol type

In commit 4233dfd7c097 ("ANDROID: SoC: core: Introduce macro
SOC_SINGLE_MULTI_EXT") a new symbol was exported, but it should have
been set as a _GPL symbol.

Fix this up by properly changing the export type.

Bug: 144610828
Cc: Banajit Goswami <bgoswami@codeaurora.org>
Cc: Sudheer Papothi <spapothi@codeaurora.org>
Cc: Meng Wang <mwang@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I373a8d347a07e3ea44af4e8c683a71c7821b6cc5