rust: time: Add __rust_helper to helpers

This is needed to inline these helpers into Rust code.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20260105-define-rust-helper-v2-22-51da5f454a67@google.com

Author: Darksonn

rust/helpers/time.c

@@ -4,37 +4,37 @@
 #include <linux/ktime.h>
 #include <linux/timekeeping.h>
 
-void rust_helper_fsleep(unsigned long usecs)
+__rust_helper void rust_helper_fsleep(unsigned long usecs)
 {
 	fsleep(usecs);
 }
 
-ktime_t rust_helper_ktime_get_real(void)
+__rust_helper ktime_t rust_helper_ktime_get_real(void)
 {
 	return ktime_get_real();
 }
 
-ktime_t rust_helper_ktime_get_boottime(void)
+__rust_helper ktime_t rust_helper_ktime_get_boottime(void)
 {
 	return ktime_get_boottime();
 }
 
-ktime_t rust_helper_ktime_get_clocktai(void)
+__rust_helper ktime_t rust_helper_ktime_get_clocktai(void)
 {
 	return ktime_get_clocktai();
 }
 
-s64 rust_helper_ktime_to_us(const ktime_t kt)
+__rust_helper s64 rust_helper_ktime_to_us(const ktime_t kt)
 {
 	return ktime_to_us(kt);
 }
 
-s64 rust_helper_ktime_to_ms(const ktime_t kt)
+__rust_helper s64 rust_helper_ktime_to_ms(const ktime_t kt)
 {
 	return ktime_to_ms(kt);
 }
 
-void rust_helper_udelay(unsigned long usec)
+__rust_helper void rust_helper_udelay(unsigned long usec)
 {
 	udelay(usec);
 }