tests/gpio: fix test GPIO_INT_EDGE bug

When test GPIO_INT_EDGE, there is no code to skip GPIO_INT_LEVEL
and jump to the end of the function. So GPIO_INT_LEVEL will
always be checked (Besides, it't always true), even if it's
testing GPIO_INT_EDGE, which will cause GPIO_INT_EDGE cases fail.

Add a goto statement for GPIO_INT_EDGE to skip GPIO_INT_LEVEL.

Jira: ZEP-1685

Change-Id: I10ce21c04c49f34aafdc2cd2f60f3e5377d6f1f5
Signed-off-by: Qiu Peiyang <peiyangx.qiu@intel.com>