MIPS: Fix rtlx build error.

  CC      arch/mips/kernel/rtlx.o
/home/ralf/src/linux/upstream-sfr/arch/mips/kernel/rtlx.c: In function ‘file_write’:
/home/ralf/src/linux/upstream-sfr/arch/mips/kernel/rtlx.c:439:23: error: unused variable ‘rt’ [-Werror=unused-variable]
/home/ralf/src/linux/upstream-sfr/arch/mips/kernel/rtlx.c: In function ‘rtlx_module_init’:
/home/ralf/src/linux/upstream-sfr/arch/mips/kernel/rtlx.c:523:3: error: implicit declaration of function ‘set_vi_handler’ [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors

Caused by 496ad9aa [new helper:
file_inode(file)].
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/rtlx.c

@@ -437,7 +437,6 @@ static ssize_t file_write(struct file *file, const char __user * buffer,
 			  size_t count, loff_t * ppos)
 {
 	int minor = iminor(file_inode(file));
-	struct rtlx_channel *rt = &rtlx->channel[minor];
 
 	/* any space left... */
 	if (!rtlx_write_poll(minor)) {