Fix section warning:

 WARNING: arch/arm/mach-at91/built-in.o(.text+0xd74): Section mismatch in reference
        from the function init_programmable_clock()
        to the function .init.text:at91_css_to_clk()
 The function  init_programmable_clock() references
 the function __init at91_css_to_clk().
 This is often because init_programmable_clock lacks a __init
 annotation or the annotation of at91_css_to_clk is wrong.

In this case the only calls to and from init_programmable_clock()
are from code marked as "__init", so this fix is trivially correct.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: NUwe Kleine-Knig <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>