fix(buttons): Fix an I2C transaction without bus lock

The call to MAX77650_getDebounceStatusnEN0() in epic_buttons_read()
performs transactions on the I2C bus but is not guarded by locking the
I2C hwlock.  This leads to strange issues like USB mode deadlocking when
writing large files.

Widen the hwlock I2C section to encompass the MAX77650_getDebounceStatusnEN0()
call as well.  This fixes #189.

Signed-off-by: Rahix <rahix@rahix.de>

epicardium/modules/buttons.c

@@ -16,17 +16,15 @@ static const uint8_t pin_mask[] = {
 uint8_t epic_buttons_read(uint8_t mask)
 {
 	uint8_t ret = 0;
-	if (portexpander_detected() && (mask & 0x7)) {
-		hwlock_acquire(HWLOCK_I2C);
 
+	hwlock_acquire(HWLOCK_I2C);
+	if (portexpander_detected() && (mask & 0x7)) {
 		/*
 		 * Not using PB_Get() here as that performs one I2C transaction
 		 * per button.
 		 */
 		uint8_t pin_status = ~portexpander_in_get(0xFF);
 
-		hwlock_release(HWLOCK_I2C);
-
 		for (uint8_t m = 1; m < 0x8; m <<= 1) {
 			if (mask & m && pin_status & pin_mask[m]) {
 				ret |= m;
@@ -38,5 +36,6 @@ uint8_t epic_buttons_read(uint8_t mask)
 		ret |= BUTTON_RESET;
 	}
 
+	hwlock_release(HWLOCK_I2C);
 	return ret;
 }