Bluetooth: shell: gatt_read: Reset offset to 0
Bluetooth: shell: gatt_read: Reset offset to 0

Unless offset was specified, it should default to 0, whereas
previously, value from the last command was used.

Signed-off-by: Paul Sokolovsky <35cb557f011771c94f127d6fef99f804b62203f5@linaro.org>

fbsder/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,ldts/zephyr,runchip/zephyr-cc3220,aceofall/zephyr-iotos,punitvara/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,mbolivar/zephyr,galak/zephyr,rsalveti/zephyr,finikorg/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3220,rsalveti/zephyr,explora26/zephyr,kraj/zephyr,galak/zephyr,kraj/zephyr,ldts/zephyr,explora26/zephyr,aceofall/zephyr-iotos,runchip/zephyr-cc3220,punitvara/zephyr,ldts/zephyr,nashif/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,fbsder/zephyr,zephyriot/zephyr,fbsder/zephyr,explora26/zephyr,zephyriot/zephyr,punitvara/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,fbsder/zephyr,ldts/zephyr,nashif/zephyr,rsalveti/zephyr,Vudentz/zephyr,rsalveti/zephyr,ldts/zephyr,finikorg/zephyr,Vudentz/zephyr,kraj/zephyr,nashif/zephyr,nashif/zephyr,punitvara/zephyr,runchip/zephyr-cc3220,GiulianoFranchetto/zephyr,rsalveti/zephyr,Vudentz/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,fbsder/zephyr,kraj/zephyr,explora26/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,nashif/zephyr,zephyriot/zephyr,mbolivar/zephyr,Vudentz/zephyr