powerpc/44x: fix spelling mistake in Kconfig "varients" -> "variants"

There is a spelling mistake in the Kconfig help text. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201216113608.11812-1-colin.king@canonical.com