clk: at91: fix h32mx prototype inclusion in pmc header

Trivial fix that prevents to compile this pmc clock driver if h32mx clock is
present but smd clock isn't.

Signed-off-by: Nicolas Ferre <[e-mail]>
Signed-off-by: Boris Brezillon <[e-mail]>
Acked-by: Alexandre Belloni <[e-mail]>
Fixes: bcc5fd49a0fd ("clk: at91: add a driver for the h32mx clock")
Cc: <[e-mail]> # 3.18+

drivers/clk/at91/pmc.h

···
 					       struct at91_pmc *pmc);
 #endif
 
-#if defined(CONFIG_HAVE_AT91_SMD)
+#if defined(CONFIG_HAVE_AT91_H32MX)
 extern void __init of_sama5d4_clk_h32mx_setup(struct device_node *np,
 					      struct at91_pmc *pmc);
 #endif