Fix typo.

(Imported from upstream's ec3a7c9b3729cd45c550222556100666aedc5bbc.)

Change-Id: I9f281fc03e6ece628d46344cf2c0850dd3bcd703
Reviewed-on: https://boringssl-review.googlesource.com/6343
Reviewed-by: Adam Langley <alangley@gmail.com>
diff --git a/crypto/aes/asm/aesni-x86.pl b/crypto/aes/asm/aesni-x86.pl
index f67df8c..9b2e37a 100644
--- a/crypto/aes/asm/aesni-x86.pl
+++ b/crypto/aes/asm/aesni-x86.pl
@@ -88,7 +88,7 @@
 $inout4="xmm6";	$in0="xmm6";
 $inout5="xmm7";	$ivec="xmm7";
 
-# AESNI extenstion
+# AESNI extension
 sub aeskeygenassist
 { my($dst,$src,$imm)=@_;
     if ("$dst:$src" =~ /xmm([0-7]):xmm([0-7])/)