[ARM] i.MX: fix breakage from commit 27889273

Fix breakage from commit 27889273

:
    i.MX Framebuffer: rename imxfb_mach_info to imx_fb_platform_data

Forgot to rename the parts in arch/arm/mach-imx/generic.c

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>