ARM: OMAP2+: fix missing variable declaration

ARM: OMAP2+: fix missing variable declaration

The function that was added doesn't actually build:

arch/arm/mach-omap2/display.c: In function 'omapdss_init_fbdev':
arch/arm/mach-omap2/display.c:184:2: error: 'r' undeclared (first use in this function)

This adds a declaration for 'r' to fix it.

Fixes: 5ce783025c82 ("ARM: OMAP2+: Don't register omapdss device for omapdrm")
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Acked-by: Tony Lindgren <[email protected]>
Signed-off-by: Tomi Valkeinen <[email protected]>