err.h: IS_ERR() can accept __user pointers

Sparse generates a false positive when you pass a __user or __iomem
pointer to the IS_ERR() functions.

  drivers/rtc/rtc-ds1286.c:344:36: sparse: incorrect type in argument 1 (different address spaces)
  drivers/rtc/rtc-ds1286.c:344:36:    expected void const *ptr
  drivers/rtc/rtc-ds1286.c:344:36:    got unsigned int [noderef] [usertype] <asn:2>*rtcregs

We can silence these by adding a __force here and upgrading to Sparse
v0.4.5-rc1 or later.

This change has no effect when using current Sparse releases.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Christopher Li <sparse@chrisli.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/err.h

@@ -24,17 +24,17 @@ static inline void * __must_check ERR_PTR(long error)
 	return (void *) error;
 }
 
-static inline long __must_check PTR_ERR(const void *ptr)
+static inline long __must_check PTR_ERR(__force const void *ptr)
 {
 	return (long) ptr;
 }
 
-static inline long __must_check IS_ERR(const void *ptr)
+static inline long __must_check IS_ERR(__force const void *ptr)
 {
 	return IS_ERR_VALUE((unsigned long)ptr);
 }
 
-static inline long __must_check IS_ERR_OR_NULL(const void *ptr)
+static inline long __must_check IS_ERR_OR_NULL(__force const void *ptr)
 {
 	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
 }
@@ -46,13 +46,13 @@ static inline long __must_check IS_ERR_OR_NULL(const void *ptr)
  * Explicitly cast an error-valued pointer to another pointer type in such a
  * way as to make it clear that's what's going on.
  */
-static inline void * __must_check ERR_CAST(const void *ptr)
+static inline void * __must_check ERR_CAST(__force const void *ptr)
 {
 	/* cast away the const */
 	return (void *) ptr;
 }
 
-static inline int __must_check PTR_RET(const void *ptr)
+static inline int __must_check PTR_RET(__force const void *ptr)
 {
 	if (IS_ERR(ptr))
 		return PTR_ERR(ptr);