Fix the test for the AST2200 in the DRAM initialization. The value
in ast->chip has to be compared against an enum constant instead of
a numerical value.

This bug got introduced when the driver was first imported into the
kernel.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 312fec14 ("drm: Initial KMS driver for AST (ASpeed Technologies) 2000 series (v2)")
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.5+
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com> # AST2600
Link: https://patchwork.freedesktop.org/patch/msgid/20230621130032.3568-2-tzimmermann@suse.de