Fix typos prior to release

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/include/mbedtls/rsa.h b/include/mbedtls/rsa.h
index 002551f..2bfaf8f 100644
--- a/include/mbedtls/rsa.h
+++ b/include/mbedtls/rsa.h
@@ -239,7 +239,7 @@
  * \param N        The RSA modulus. This may be \c NULL.
  * \param N_len    The Byte length of \p N; it is ignored if \p N == NULL.
  * \param P        The first prime factor of \p N. This may be \c NULL.
- * \param P_len    The Byte length of \p P; it ns ignored if \p P == NULL.
+ * \param P_len    The Byte length of \p P; it is ignored if \p P == NULL.
  * \param Q        The second prime factor of \p N. This may be \c NULL.
  * \param Q_len    The Byte length of \p Q; it is ignored if \p Q == NULL.
  * \param D        The private exponent. This may be \c NULL.