edgetpu: fix compiler warnings (W=1)

edgetpu-firmware-util.c:12:7: error: no previous prototype for function 'edgetpu_fwutil_name_from_attr_buf' [-Werror,-Wmissing-prototypes]
char *edgetpu_fwutil_name_from_attr_buf(const char *buf)
      ^
edgetpu-firmware-util.c:12:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
char *edgetpu_fwutil_name_from_attr_buf(const char *buf)
^
static
abrolhos-firmware.c:109:5: error: no previous prototype for function 'abrolhos_edgetpu_firmware_create' [-Werror,-Wmissing-prototypes]
int abrolhos_edgetpu_firmware_create(struct edgetpu_dev *etdev)
    ^
abrolhos-firmware.c:109:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
int abrolhos_edgetpu_firmware_create(struct edgetpu_dev *etdev)
^
static
abrolhos-firmware.c:114:6: error: no previous prototype for function 'abrolhos_edgetpu_firmware_destroy' [-Werror,-Wmissing-prototypes]
void abrolhos_edgetpu_firmware_destroy(struct edgetpu_dev *etdev)
     ^
abrolhos-firmware.c:114:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
void abrolhos_edgetpu_firmware_destroy(struct edgetpu_dev *etdev)
^
static
>-------if (ret) {
abrolhos-pm.c:67:53: error: format specifies type 'int' but the argument has type 'u64' (aka 'unsigned long long') [-Werror,-Wformat]
        dev_dbg(dev, "Power state %d -> %d\n", curr_state, val);
                                        ~~                 ^~~
                                        %llu
abrolhos-pm.c:105:5: error: no previous prototype for function 'abrolhos_pwr_policy_set' [-Werror,-Wmissing-prototypes]
int abrolhos_pwr_policy_set(void *data, u64 val)
    ^
abrolhos-pm.c:105:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
int abrolhos_pwr_policy_set(void *data, u64 val)
^
static

Signed-off-by: Patrick Tjin <pattjin@google.com>
Change-Id: Ie263785f9657a68ff37d0109b9c157691ebf2040