crypto: essiv - fix AEAD capitalization and preposition use in help text

crypto: essiv - fix AEAD capitalization and preposition use in help text

BugLink: https://bugs.launchpad.net/bugs/1864488
[ Upstream commit ab3d436bf3e9d05f58ceaa85ff7475bfcd6e45af ]

"AEAD" is capitalized everywhere else.
Use "an" when followed by a written or spoken vowel.

Fixes: be1eb7f78aa8fbe3 ("crypto: essiv - create wrapper template for ESSIV generation")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>