serial: fsl_lpuart: Fix comment typo

The double `as' is duplicated in the comment, remove one.

Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Link: https://lore.kernel.org/r/20220803104208.4127-1-wangborong@cdjrlc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>