powerpc: Rename thread_struct.fs to addr_limit

It's called 'fs' for historical reasons, it's named after the x86 'FS'
register. But we don't have to use that name for the member of
thread_struct, and in fact arch/x86 doesn't even call it 'fs' anymore.

So rename it to 'addr_limit', which better reflects what it's used
for, and is also the name used on other arches.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/uaccess.h

@@ -30,8 +30,8 @@
 #endif
 
 #define get_ds()	(KERNEL_DS)
-#define get_fs()	(current->thread.fs)
-#define set_fs(val)	(current->thread.fs = (val))
+#define get_fs()	(current->thread.addr_limit)
+#define set_fs(val)	(current->thread.addr_limit = (val))
 
 #define segment_eq(a, b)	((a).seg == (b).seg)