drm/gpuvm: fix various typos in .c and .h gpuvm file

After working with this code for a while, I came across several typos.
This patch fixes them.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250825-gpuvm-typo-fix-v1-1-14e9e78e28e6@google.com


Signed-off-by: Danilo Krummrich <dakr@kernel.org>