MIPS: Spelling fix lets -> let's

As noticed by Sergei in the discussion of Andrea Gelmini's patch series.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>

arch/mips/sgi-ip27/ip27-xtalk.c

@@ -67,7 +67,7 @@ static int xbow_probe(nasid_t nasid)
 		return -ENODEV;
 
 	/*
-	 * Okay, here's a xbow. Lets arbitrate and find
+	 * Okay, here's a xbow. Let's arbitrate and find
 	 * out if we should initialize it. Set enabled
 	 * hub connected at highest or lowest widget as
 	 * master.