OWNERS: Add Pavithra as a reviewer

I have been actively contributing to OpenBMC/PLDM for quite
some time now. Attached is a summary of my contributions to
the repository [1].

I would like to learn and help out on pldm reviews.

[1]: https://github.com/openbmc/pldm/commits?author=Pavithrab7



Change-Id: I374c55f7e01a7648010c2964b3cd60d5deb0ef57
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>