tile: fix tilegx vmalloc_sync_all BUG_ON
tile: fix tilegx vmalloc_sync_all BUG_ON

As specified, the test wasn't correct, and in any case it should
be a BUILD_BUG_ON.

Signed-off-by: Chris Metcalf <074881f6f5da4d3b5278870ff234d1077ee622c0@tilera.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs