Fix no-ec2m in ec_curve.c (1.1.0)

I made a mistake in d4a5dac9 and
inverted the GF2m and GFp calls in ec_point_get_affine_coordinates, this
fixes it.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9873)