uaccess: gate _copy_[to|from]_user on !INLINE_COPY_FROM_USER

These methods only exist when INLINE_COPY_FROM_USER is disabled, so update
the header file to reflect that.

This fixes the following error on builds that enable both RUST and
INLINE_COPY_FROM_USER.

ERROR: modpost: "_copy_from_user" [samples/rust/rust_misc_device.ko] undefined!
ERROR: modpost: "_copy_to_user" [samples/rust/rust_misc_device.ko] undefined!

This error is triggered because when a method is available both as a
rust_helper_* and normal method, Rust will call the normal method.

[[e-mail]: s/INLINE_COPY_FROM_USER/INLINE_COPY_TO_USER/, per Alice]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: d99dc586ca7c ("uaccess: decouple INLINE_COPY_FROM_USER and CONFIG_RUST")
Signed-off-by: Alice Ryhl <[e-mail]>
Cc: Alex Gaynor <[e-mail]>
Cc: Andreas Hindborg <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Björn Roy Baron <[e-mail]>
Cc: Boqun Feng <[e-mail]>
Cc: Danilo Krummrich <[e-mail]>
Cc: Gary Guo <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Miguel Ojeda <[e-mail]>
Cc: Trevor Gross <[e-mail]>
Cc: Yury Norov (NVIDIA) <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/uaccess.h

···
 	memset(to + (n - res), 0, res);
 	return res;
 }
+#ifndef INLINE_COPY_FROM_USER
 extern __must_check unsigned long
 _copy_from_user(void *, const void __user *, unsigned long);
+#endif
 
 static inline __must_check unsigned long
 _inline_copy_to_user(void __user *to, const void *from, unsigned long n)
···
 	}
 	return n;
 }
+#ifndef INLINE_COPY_TO_USER
 extern __must_check unsigned long
 _copy_to_user(void __user *, const void *, unsigned long);
+#endif
 
 static __always_inline unsigned long __must_check
 copy_from_user(void *to, const void __user *from, unsigned long n)