Fix minor issues in SHA1 documentation
diff --git a/include/mbedtls/sha1.h b/include/mbedtls/sha1.h
index 0979dc0..2c4f0a6 100644
--- a/include/mbedtls/sha1.h
+++ b/include/mbedtls/sha1.h
@@ -160,7 +160,6 @@
*
* \param ctx The SHA-1 context to use. This must be initialized and
* have a hash operation started.
- * This must not be \c NULL.
* \param output The SHA-1 checksum result. This must be a writable
* buffer of length \c 20 Bytes.
*
@@ -177,8 +176,8 @@
* constitutes a security risk. We recommend considering
* stronger message digests instead.
*
- * \param ctx The SHA-1 context to use. This must be initialized and
- * have a hash operation started.
+ * \param ctx The SHA-1 context to use. This must be initialized
+ * and have a hash operation started.
* \param data The data block being processed. This must be a
* readable buffer of length \c 64 Bytes.
*
@@ -219,7 +218,7 @@
*
* \deprecated Superseded by mbedtls_sha1_update_ret() in 2.7.0.
*
- * \param ctx The SHA-1 context. THis must be initialized and
+ * \param ctx The SHA-1 context. This must be initialized and
* have a hash operation started.
* \param input The buffer holding the input data.
* This must be a readable buffer of length \p ilen Bytes.