Revert "Change env_get_char from a global function ptr to a function."

This reverts commit c0559be371b2a64b1a817088c3308688e2182f93
which is known to break booting from dataflash and NAND.
diff --git a/common/env_eeprom.c b/common/env_eeprom.c
index fae87ca..2adc129 100644
--- a/common/env_eeprom.c
+++ b/common/env_eeprom.c
@@ -38,6 +38,7 @@
 
 char * env_name_spec = "EEPROM";
 
+extern uchar (*env_get_char)(int);
 extern uchar env_get_char_memory (int index);