docs: Fix typo in scalar-functions.rst (#11582)

Summary:
"deafult" --> "default"

Pull Request resolved: #11582

Reviewed By: kagamiori

Differential Revision: D67457483

Pulled By: pedroerp

fbshipit-source-id: d4be2bbe7e32891777caea8d994ed8c5f49be983

velox/docs/develop/scalar-functions.rst

@@ -151,7 +151,7 @@ Null-Free Fast Path
 A "callNullFree" function may be implemented in place of or along side "call"
 and/or "callNullable" functions. When only the "callNullFree" function is
 implemented, evaluation of the function will be skipped and null will
-automatically be produced if any of the input arguments are null (like deafult
+automatically be produced if any of the input arguments are null (like default
 null behavior) or if any of the input arguments are of a complex type and
 contain null anywhere in their value, e.g. an array that has a null element.
 If "callNullFree" is implemented alongside "call" and/or "callNullable", an