[ARM] Fix warning in arch/arm/mach-sa1100/generic.c

Fix:

arch/arm/mach-sa1100/generic.c:224: warning: 'struct mcp_plat_data' declared inside parameter list

caused by mussing structure and function declaration.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-sa1100/generic.h

@@ -39,3 +39,6 @@ extern void sa11x0_set_ssp_data(struct sa11x0_ssp_plat_ops *ops);
 
 struct irda_platform_data;
 void sa11x0_set_irda_data(struct irda_platform_data *irda);
+
+struct mcp_plat_data;
+void sa11x0_set_mcp_data(struct mcp_plat_data *data);