MIPS: Loongson: Fix GCC 2.6.0 build error.

CC      arch/mips/loongson/common/env.o
arch/mips/loongson/common/env.c: In function 'prom_init_env':
arch/mips/loongson/common/env.c:50:12: error: variable 'ret' set but not used [-Werror=unused-but-set-variable]
arch/mips/loongson/common/env.c:51:12: error: variable 'ret' set but not used [-Werror=unused-but-set-variable]
arch/mips/loongson/common/env.c:52:12: error: variable 'ret' set but not used [-Werror=unused-but-set-variable]
arch/mips/loongson/common/env.c:53:12: error: variable 'ret' set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson/common/env.c

@@ -29,9 +29,10 @@ unsigned long memsize, highmemsize;
 
 #define parse_even_earlier(res, option, p)				\
 do {									\
-	int ret;							\
+	unsigned int tmp __maybe_unused;				\
+									\
 	if (strncmp(option, (char *)p, strlen(option)) == 0)		\
-		ret = strict_strtol((char *)p + strlen(option"="), 10, &res); \
+		tmp = strict_strtol((char *)p + strlen(option"="), 10, &res); \
 } while (0)
 
 void __init prom_init_env(void)