Add missing return values for fx_directory_create api (#6)

Co-authored-by: Frédéric Desbiens <frederic.desbiens@eclipse-foundation.org>

Author: ayedm1

rtos-docs/filex/chapter4.adoc

@@ -276,6 +276,10 @@ This service creates a subdirectory in the current default directory or in the p
 * *FX_PTR_ERROR* (0x18) Invalid media pointer
 * *FX_INVALID_ATTR* (0x19) Invalid attributes selected.
 * *FX_CALLER_ERROR* (0x20) Caller is not a thread.
+* *FX_INVALID_NAME** (0x0C) New directory name is invalid.
+* *FX_WRITE_PROTECT** (0x23) Specified media is write protected.
+* *FX_ALREADY_CREATED** (0x0B) Specified directory was already created.
+* *FX_INVALID_PATH** (0x0D) Path is invalid.
 
 === Allowed From