Mark discriminant as inline

This function is very simple, ideally it should be some form of language
intrinsics, but here we are. I could try and see if ther are cases where
compiler wouldn't inline this function. Instead I just put the attribute
... and move on doing something else

Signed-off-by: Ahmed Abdelraoof <[email protected]>

safe-discriminant/src/lib.rs

@@ -55,6 +55,7 @@ pub unsafe trait Discriminant {
     /// `#[repr(u*)]` or `#[repr(i*)]`.
     type Selector: Copy;
     /// Returns the discriminant value of enum variant we are using.
+    #[inline(always)]
     fn discriminant(&self) -> Self::Selector {
         unsafe { *<*const _>::from(self).cast() }
     }