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>
diff --git a/arch/mips/sgi-ip27/ip27-nmi.c b/arch/mips/sgi-ip27/ip27-nmi.c
index a2358b4..cfceaea 100644
--- a/arch/mips/sgi-ip27/ip27-nmi.c
+++ b/arch/mips/sgi-ip27/ip27-nmi.c
@@ -23,7 +23,7 @@
 static arch_spinlock_t nmi_lock = __ARCH_SPIN_LOCK_UNLOCKED;
 
 /*
- * Lets see what else we need to do here. Set up sp, gp?
+ * Let's see what else we need to do here. Set up sp, gp?
  */
 void nmi_dump(void)
 {