cmd_fat.c: fix build warning

Commit cfda5aeab89d73779e26f0d34cf10f64caa67431
(cmd_fat: use common get_device_and_partition function)
introduced a warning:
cmd_fat.c: In function 'do_fat_fswrite':
cmd_fat.c:178:8: warning: unused variable 'ep' [-Wunused-variable]

Fix it.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reported-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
Tested-by: Albert ARIBAUD <albert.u.boot@aribaud.net>

common/cmd_fat.c

@@ -175,7 +175,6 @@ static int do_fat_fswrite(cmd_tbl_t *cmdtp, int flag,
 	disk_partition_t info;
 	int dev = 0;
 	int part = 1;
-	char *ep;
 
 	if (argc < 5)
 		return cmd_usage(cmdtp);