drm/gma500: remove set but not used variable 'is_hdmi','is_crt'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/gma500/cdv_intel_display.c: In function cdv_intel_crtc_mode_set:
drivers/gpu/drm/gma500/cdv_intel_display.c:594:7: warning: variable is_hdmi set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/gma500/cdv_intel_display.c: In function cdv_intel_crtc_mode_set:
drivers/gpu/drm/gma500/cdv_intel_display.c:593:7: warning: variable is_crt set but not used [-Wunused-but-set-variable]

They are not used since commit acd7ef92 ("gma500:
Update the Cedarview clock handling")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1573828027-122323-4-git-send-email-zhengbin13@huawei.com