trivial: fix typo 'an host'

In English, unlike in French, the 'h' in 'host' is pronounced, meaning that
the article should be 'a' instead of 'an'.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/package/pkg-autotools.mk b/package/pkg-autotools.mk
index 4443c72..db3736c 100644
--- a/package/pkg-autotools.mk
+++ b/package/pkg-autotools.mk
@@ -54,7 +54,7 @@
 # make targets
 #
 #  argument 1 is the lowercase package name
-#  argument 2 is the uppercase package name, including an HOST_ prefix
+#  argument 2 is the uppercase package name, including a HOST_ prefix
 #             for host packages
 #  argument 3 is the uppercase package name, without the HOST_ prefix
 #             for host packages