rust: error: modify from_errno to use try_from_errno

Modify the from_errno function to use try_from_errno to
reduce code duplication while still maintaining all existing
behavior and error handling and also reduces unsafe code.

Link: Rust-for-Linux#1125
Suggested-by: Miguel Ojeda <[email protected]>
Co-developed-by: Guilherme Augusto Martins da Silva <[email protected]>
Signed-off-by: Guilherme Augusto Martins da Silva <[email protected]>
Signed-off-by: Daniel Sedlak <[email protected]>
Reviewed-by: Fiona Behrens <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: wutchzone

rust/kernel/error.rs

@@ -101,19 +101,16 @@ impl Error {
     /// It is a bug to pass an out-of-range `errno`. `EINVAL` would
     /// be returned in such a case.
     pub fn from_errno(errno: crate::ffi::c_int) -> Error {
-        if errno < -(bindings::MAX_ERRNO as i32) || errno >= 0 {
+        if let Some(error) = Self::try_from_errno(errno) {
+            error
+        } else {
             // TODO: Make it a `WARN_ONCE` once available.
             crate::pr_warn!(
                 "attempted to create `Error` with out of range `errno`: {}",
                 errno
             );
-            return code::EINVAL;
+            code::EINVAL
         }
-
-        // INVARIANT: The check above ensures the type invariant
-        // will hold.
-        // SAFETY: `errno` is checked above to be in a valid range.
-        unsafe { Error::from_errno_unchecked(errno) }
     }
 
     /// Creates an [`Error`] from a kernel error code.