env_mmc: add mmc_get_env_addr() prototype

Add missing mmc_get_env_addr() prototype in environment.h

Signed-off-by: Dmitry Lifshitz <lifshitz@compulab.co.il>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>

include/environment.h

@@ -180,6 +180,12 @@ extern unsigned char env_get_char_spec(int);
 extern void env_reloc(void);
 #endif
 
+#ifdef CONFIG_ENV_IS_IN_MMC
+#include <mmc.h>
+
+extern int mmc_get_env_addr(struct mmc *mmc, int copy, u32 *env_addr);
+#endif
+
 #ifndef DO_DEPS_ONLY
 
 #include <env_attr.h>