userspace: remove dead code
userspace: remove dead code

File userspace.c contains dead code in function char *otype_to_str()
Remove "return NULL" and replace with "ret = NULL".

Found as a coding guideline violation (MISRA R2.1) by static
coding scanning tool.

Signed-off-by: Maksim Masalski <00762c94550ce68b2a0e3f1373f5a19cd4f4bbbb@intel.com>

galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr