rust: num: fix typos in Bounded documentation

rust: num: fix typos in Bounded documentation

Fix several typos and grammatical errors in the Bounded type documentation:
- "less significant bits" -> "least significant bits"
- "with in" -> "within"
- "withheld" -> "upheld"
- "//  This" -> "// This" (double space)
- "doesn't fits" -> "doesn't fit" (2 occurrences)

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: https://github.com/Rust-for-Linux/linux/issues/1210
Signed-off-by: Nakamura Shuta <nakamura.shuta@gmail.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Yury Norov (NVIDIA) <yury.norov@nvidia.com>
Fixes: 01e345e82ec3 ("rust: num: add Bounded integer wrapping type")
Link: https://patch.msgid.link/20251204024336.246587-1-nakamura.shuta@gmail.com
[ Removed Link tag due to duplicated URL. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>