ANDROID: iommu: fix export symbol type

In commit 91740f19 ("FROMLIST: drivers/iommu: Export core IOMMU API
symbols to permit modular drivers") 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: 140290589
Cc: Will Deacon <willdeacon@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I5c1a4ac3dcaa1362c43b103c80ca278b2174039f