rpmsg: fix a comment typo for rpmsg_device_match()

Should be 'a' rather than 'an'.
Signed-off-by: WANG Wenhu <wenhu.wang@vivo.com>
Link: https://lore.kernel.org/r/20200313165049.62907-1-wenhu.wang@vivo.comSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/rpmsg_core.c

@@ -284,7 +284,7 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
 EXPORT_SYMBOL(rpmsg_trysend_offchannel);
 
 /*
- * match an rpmsg channel with a channel info struct.
+ * match a rpmsg channel with a channel info struct.
  * this is used to make sure we're not creating rpmsg devices for channels
  * that already exist.
  */