rust: kunit: use core::ffi::CStr method names

Prepare for `core::ffi::CStr` taking the place of `kernel::str::CStr` by
avoid methods that only exist on the latter.

Link: Rust-for-Linux#1075
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: tamird

rust/kernel/kunit.rs

@@ -102,12 +102,12 @@ macro_rules! kunit_assert {
             unsafe impl Sync for UnaryAssert {}
 
             static LOCATION: Location = Location($crate::bindings::kunit_loc {
-                file: FILE.as_char_ptr(),
+                file: $crate::str::as_char_ptr_in_const_context(FILE),
                 line: LINE,
             });
             static ASSERTION: UnaryAssert = UnaryAssert($crate::bindings::kunit_unary_assert {
                 assert: $crate::bindings::kunit_assert {},
-                condition: CONDITION.as_char_ptr(),
+                condition: $crate::str::as_char_ptr_in_const_context(CONDITION),
                 expected_true: true,
             });
 
@@ -202,7 +202,7 @@ pub const fn kunit_case(
 ) -> kernel::bindings::kunit_case {
     kernel::bindings::kunit_case {
         run_case: Some(run_case),
-        name: name.as_char_ptr(),
+        name: kernel::str::as_char_ptr_in_const_context(name),
         attr: kernel::bindings::kunit_attributes {
             speed: kernel::bindings::kunit_speed_KUNIT_SPEED_NORMAL,
         },