mx6: clock: Add a prototype for do_mx6_showclocks()

When compiling with W=1 the following warning is observed:

arch/arm/mach-imx/mx6/clock.c:1268:5: warning: no previous prototype for ‘do_mx6_showclocks’ [-Wmissing-prototypes] int do_mx6_showclocks(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])

Remove this warning by adding the function prototype into arch-mx6/clock.h file.

Signed-off-by: Diego Dorta <diego.dorta@nxp.com>

arch/arm/include/asm/arch-mx6/clock.h

@@ -80,4 +80,5 @@ void enable_thermal_clk(void);
 void mxs_set_lcdclk(u32 base_addr, u32 freq);
 void select_ldb_di_clock_source(enum ldb_di_clock clk);
 void enable_eim_clk(unsigned char enable);
+int do_mx6_showclocks(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]);
 #endif /* __ASM_ARCH_CLOCK_H */