Fix typo in a comment

Co-authored-by: Janos Follath <janos.follath@arm.com>
diff --git a/library/ecp.c b/library/ecp.c
index 67f399f..82c931f 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -130,7 +130,7 @@
 #if !defined(MBEDTLS_ECP_NO_INTERNAL_RNG)
 /*
  * Currently ecp_mul() takes a RNG function as an argument, used for
- * side-channel protection, but it can be NULL. The initial reasonning was
+ * side-channel protection, but it can be NULL. The initial reasoning was
  * that people will pass non-NULL RNG when they care about side-channels, but
  * unfortunately we have some APIs that call ecp_mul() with a NULL RNG, with
  * no opportunity for the user to do anything about it.