Rename getenv_r() into getenv_f()

While running from flash, i. e. before relocation, we have only a
limited C runtime environment without writable data segment. In this
phase, some configurations (for example with environment in EEPROM)
must not use the normal getenv(), but a special function.  This
function had been called getenv_r(), with the idea that the "_r"
suffix would mean the same as in the _r_eentrant versions of some of
the C library functions (for example getdate vs. getdate_r, getgrent
vs. getgrent_r, etc.).

Unfortunately this was a misleading name, as in U-Boot the "_r"
generally means "running from RAM", i. e. _after_ relocation.

To avoid confusion, rename into getenv_f() [as "running from flash"]

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>
diff --git a/board/esd/canbt/canbt.c b/board/esd/canbt/canbt.c
index bfec548..0d2d7f1 100644
--- a/board/esd/canbt/canbt.c
+++ b/board/esd/canbt/canbt.c
@@ -157,7 +157,7 @@
 	int index;
 	int len;
 	char str[64];
-	int i = getenv_r ("serial#", str, sizeof (str));
+	int i = getenv_f("serial#", str, sizeof (str));
 
 	puts ("Board: ");