Fix doc of `llvm.bitreverse.iN`
Fix doc of `llvm.bitreverse.iN`

Summary:
The return type is `iN` rather than always `i16`

Seems to be a typo in https://reviews.llvm.org/rL252878 .

Reviewers: jmolloy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D27047

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@287769 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm