[PATCH] Documentation: fix spelling errors in iommufd.rst

[Alessandro Ratti <alessandro@xxxxxxxxx>]

Hi,

While working on a task for the Linux Kernel Mentorship Program, I scanned the
kernel documentation using `codespell` to identify any outstanding spelling
mistakes.

During the process, I discovered two typos in `Documentation/userspace-api/iommufd.rst`:

  - "primarly" → "primarily"
  - "sharable" → "shareable"

This patch corrects these minor errors. I’ve excluded already translated and
autogenerated files from the scan to avoid false positives. The command used
was:

  codespell Documentation \
    -S "Documentation/translations/*,**/_build/*,**/*.po,**/*.pot,**/*.pdf,**/*.svg" \
    -L "te,fo,uefi,sysfs,procfs,virtio,irq,skb,uname,userspace,nd"

Patch applies cleanly on top of mainline.

Thanks for your time and consideration.

Best regards,  
Alessandro