gpu: nova-core: bitfield: fix broken Default implementation

The current implementation does not actually set the default values for
the fields in the bitfield.

Fixes: 3fa145b ("gpu: nova-core: register: generate correct `Default` implementation")
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260401-fix-bitfield-v2-1-2fa68c98114a@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Eliot Courtney

drivers/gpu/nova-core/bitfield.rs

@@ -314,12 +314,11 @@ macro_rules! bitfield {
         /// Returns a value for the bitfield where all fields are set to their default value.
         impl ::core::default::Default for $name {
             fn default() -> Self {
-                #[allow(unused_mut)]
-                let mut value = Self(Default::default());
+                let value = Self(Default::default());
 
                 ::kernel::macros::paste!(
                 $(
-                value.[<set_ $field>](Default::default());
+                let value = value.[<set_ $field>](Default::default());
                 )*
                 );