Fix build breakage casued by commit c0559be371

Change env_get_char from a global function ptr to a function.

Signed-off-by: Wolfgang Denk <wd@denx.de>

common/cmd_bootm.c

@@ -100,7 +100,6 @@ int do_bootvx (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]);
 int do_bootelf (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]);
 #endif
 #if defined(CONFIG_ARTOS) && defined(CONFIG_PPC)
-extern uchar (*env_get_char)(int); /* Returns a character from the environment */
 static boot_os_fn do_bootm_artos;
 #endif