rust: block: simplify Result<()> in validate_block_size return

`Result` is used in place of `Result<()>` because the default type
parameters are unit `()` and `Error` types, which are automatically
inferred. Thus keep the usage consistent throughout codebase.

Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Link: #1128
Signed-off-by: Manas <manas18244@iiitd.ac.in>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/r/20241118-simplify-result-v3-1-6b1566a77eab@iiitd.ac.in
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: weirdsmiley

rust/kernel/block/mq/gen_disk.rs

@@ -45,7 +45,7 @@ impl GenDiskBuilder {
 
     /// Validate block size by verifying that it is between 512 and `PAGE_SIZE`,
     /// and that it is a power of two.
-    fn validate_block_size(size: u32) -> Result<()> {
+    fn validate_block_size(size: u32) -> Result {
         if !(512..=bindings::PAGE_SIZE as u32).contains(&size) || !size.is_power_of_two() {
             Err(error::code::EINVAL)
         } else {