MIPS: BCM47xx: Fix nvram_getenv return value.

Nvram_getenv should behave like cfe_getenv. cfe_getenv returns 0 on
success and -9 if the value was not found. If the input was wrong -8
will be returned by cfe_getenv.  Change nvram_getenv to do the same.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: Waldemar Brodkorb <wbx@openadk.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1520/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mach-bcm47xx/nvram.h

@@ -31,6 +31,9 @@ struct nvram_header {
 #define NVRAM_MAX_VALUE_LEN 255
 #define NVRAM_MAX_PARAM_LEN 64
 
+#define NVRAM_ERR_INV_PARAM	-8
+#define NVRAM_ERR_ENVNOTFOUND	-9
+
 extern int nvram_getenv(char *name, char *val, size_t val_len);
 
 #endif