samples: basic: blinky_pwm: fix bad path in README
samples: basic: blinky_pwm: fix bad path in README

The README gives as example the command to build
the sample with west. The path of the sample as
stated does not exist. This fixes it to blinky_pwm.

Signed-off-by: Jennifer Williams <7953176682adde4345743ea99dbf2682fb898b9d@intel.com>

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