OvmfPkg/SerializeVariablesLib: convert line endings to uniform CRLF

"SerializeVariablesLib.h" is pure LF, while "SerializeVariablesLib.c" is
mixed (its only CRLF terminators are from commit e678f9db899ad). Convert
them both with "unix2dos".

"git show -b" produces no code hunks for this patch. Due to its simple and
mechanic nature (and because it blocks the application of another patch),
it's being committed without review.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>