block: rnull: add missing MODULE_DESCRIPTION

Add the missing description to fix the following warning:

WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/block/rnull_mod.o

Signed-off-by: FUJITA Tomonori <[email protected]>
Acked-by: Andreas Hindborg <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: fujita

drivers/block/rnull.rs

@@ -28,6 +28,7 @@ module! {
     type: NullBlkModule,
     name: "rnull_mod",
     author: "Andreas Hindborg",
+    description: "Rust implementation of the C null block driver",
     license: "GPL v2",
 }