Use as-less cast for UTC string

Use a nicer, more specific way of casting for the UTC constant.

src/header/time/constants.rs

@@ -10,7 +10,7 @@ pub mod sys;
 #[path = "redox.rs"]
 pub mod sys;
 
-pub(crate) const UTC: *const c_char = b"UTC\0" as *const u8 as *const c_char;
+pub(crate) const UTC: *const c_char = b"UTC\0".as_ptr().cast();
 
 pub(crate) const DAY_NAMES: [&str; 7] = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
 pub(crate) const MON_NAMES: [&str; 12] = [