docs: Include uaccess docs from the right file

Documentation/core-api/kernel-api.rst was including kerneldoc comments from
arch/x86/include/asm/uaccess_32.h, but the relevant comments moved to
.../uaccess.h some time ago.  Correct the include to pick up the comments
and eliminate a warning.
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/core-api/kernel-api.rst

@@ -114,7 +114,7 @@ The Slab Cache
 User Space Memory Access
 ------------------------
 
-.. kernel-doc:: arch/x86/include/asm/uaccess_32.h
+.. kernel-doc:: arch/x86/include/asm/uaccess.h
    :internal:
 
 .. kernel-doc:: arch/x86/lib/usercopy_32.c