spmi: Fix sandbox spmi driver memory corruption

There is off-by-one error in sandbox_emul_gpio that causes
segfault of certain tests.

EMUL_GPIO_REG_END is the address of last valid (emulated) register.
This patch fixed this (by adding one more element to emulated register array).
Signed-off-by: NMateusz Kulikowski <mateusz.kulikowski@gmail.com>
Tested-by: NStephen Warren <swarren@nvidia.com>

drivers/spmi/spmi-sandbox.c

@@ -35,7 +35,8 @@ struct sandbox_emul_fake_regs {
 };
 
 struct sandbox_emul_gpio {
-	struct sandbox_emul_fake_regs r[EMUL_GPIO_REG_END]; /* Fake registers */
+	/* Fake registers - need one more entry as REG_END is valid address. */
+	struct sandbox_emul_fake_regs r[EMUL_GPIO_REG_END + 1];
 };
 
 struct sandbox_spmi_priv {