OvmfPkg/EnrollDefaultKeys: clean up acronym capitalization in identifiers

OvmfPkg/EnrollDefaultKeys: clean up acronym capitalization in identifiers

According to the edk2 coding standards, "[w]hen all letters in an acronym
are capitalized, it makes the prior and subsequent words visually
difficult to distinguish".

Fix the spellings of three acronyms, accordingly:
- "KEK" (Key Exchange Key) should be written as "Kek", in "mMicrosoftKEK",
- "CA" (Certificate Authority) should be written as "Ca", in
  "mMicrosoftUefiCA",
- "PCA" (Production Certificate Authority) should be written as "Pca", in
  "mMicrosoftPCA".

Generate the changes with:

  sed --regexp-extended --in-place \
    --expression='s,\<mMicrosoftKEK\>,mMicrosoftKek,g' \
    --expression='s,\<mMicrosoftUefiCA\>,mMicrosoftUefiCa,g' \
    --expression='s,\<mMicrosoftPCA\>,mMicrosoftPca,g' \
    OvmfPkg/EnrollDefaultKeys/EnrollDefaultKeys.c

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien.grall@arm.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1747
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Gary Lin <glin@suse.com>