Fix documentation

Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 991c169..4f2cdb3 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -2512,7 +2512,7 @@
     }
 
     /* Immediately reject a zero-length signature buffer. This guarantees
-     * that signature must be a valid pointer. (On the other hand, the hash
+     * that signature must be a valid pointer. (On the other hand, the input
      * buffer can in principle be empty since it doesn't actually have
      * to be a hash.) */
     if( signature_size == 0 )