mx5: Undeclare imx_decode_pll()

The imx_decode_pll() function does not exist for mx5, so remove its declaration.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>

arch/arm/include/asm/arch-mx5/clock.h

@@ -38,8 +38,6 @@ enum mxc_clock {
 	MXC_PERIPH_CLK,
 };
 
-unsigned int imx_decode_pll(unsigned int pll, unsigned int f_ref);
-
 u32 imx_get_uartclk(void);
 u32 imx_get_fecclk(void);
 unsigned int mxc_get_clock(enum mxc_clock clk);