serial: mvebu-uart: remove duplicated bit-wise or of STAT_FRM_ERR

Bit pattern STAT_FRM_ERR is being bit-wise or'd twice; remove the
redundant 2nd STAT_FRM_ERR

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>