ARM: omap: fix section mismatch error for omap_4430sdp_display_init()

WARNING: arch/arm/mach-omap2/built-in.o(.text+0xb798): Section mismatch in reference from the function omap_4430sdp_display_init() to the function .init.text:omap_display_init()
The function omap_4430sdp_display_init() references
the function __init omap_display_init().
This is often because omap_4430sdp_display_init lacks a __init
annotation or the annotation of omap_display_init is wrong.

Fix this by adding __init to omap_4430sdp_display_init().

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>