drivers: spi_gecko: fix duplicated variable declaration
drivers: spi_gecko: fix duplicated variable declaration

The commit 44679c7bd86c5a7f7caf58f8ce66f30a360baf27 introduced this
duplicated declaration of the local variable data.

This commit fixes this issue.

Fixes #42117

Signed-off-by: Christian Taedcke <5dfb12f5b8690cb9c18e955016e7e3173b81d0d8@lemonbeat.com>

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