capability: erase checker warnings about struct __user_cap_data_struct

Currently Sparse warns the following when compiling kernel/capability.c:

kernel/capability.c:191:35: warning: incorrect type in argument 2
(different address spaces)
kernel/capability.c:191:35: expected void const *from
kernel/capability.c:191:35: got struct __user_cap_data_struct
[noderef] __user *
kernel/capability.c:168:14: warning: dereference of noderef expression
...... (multiple noderef warnings on different locations)
kernel/capability.c:244:29: warning: incorrect type in argument 1
(different address spaces)
kernel/capability.c:244:29: expected void *to
kernel/capability.c:244:29: got struct __user_cap_data_struct
[noderef] __user ( * )[2]
kernel/capability.c:247:42: warning: dereference of noderef expression
...... (multiple noderef warnings on different locations)

It seems that defining `struct __user_cap_data_struct` together with
`cap_user_data_t` make Sparse believe that the struct is `noderef` as
well. Separate their definitions to clarify their respective attributes.

Signed-off-by: GONG, Ruiqi <[e-mail]>
Acked-by: Serge Hallyn <[e-mail]>
[PM: wrapped long lines in the description]
Signed-off-by: Paul Moore <[e-mail]>

include/uapi/linux/capability.h

···
 	int pid;
 } __user *cap_user_header_t;
 
-typedef struct __user_cap_data_struct {
+struct __user_cap_data_struct {
         __u32 effective;
         __u32 permitted;
         __u32 inheritable;
-} __user *cap_user_data_t;
+};
+typedef struct __user_cap_data_struct __user *cap_user_data_t;
 
 
 #define VFS_CAP_REVISION_MASK	0xFF000000