mach: prevent UART3 from being disabled by the hwmod

Signed-off-by: David Rodero <david@codiguiel.net>

Conflicts:
	arch/arm/mach-omap2/omap_hwmod.c
	arch/arm/mach-omap2/omap_hwmod_3xxx_data.c
	arch/arm/mach-omap2/serial.c
mach: prevent disabling uart clock

Signed-off-by: David Rodero <david@codiguiel.net>