[PATCH] fs/super.c: unexport user_get_super

There's no modular usage in the kernel and modules shouldn't use this
symbol.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>