Staging: iio: use !x instead of x == NULL

Functions like devm_kzalloc, kmalloc_array, devm_ioremap,
usb_alloc_urb, alloc_netdev return NULL as a return value on failure.
Generally, When NULL represents failure, !x is commonly used.

This patch cleans up the tests on the results of these functions, thereby
using !x instead of x == NULL or NULL == x. This is done via following
coccinelle script:
@prob_7@
identifier x;
statement S;
@@

(
 x = devm_kzalloc(...);
|
 x = usb_alloc_urb(...);
|
 x = kmalloc_array(...);
|
 x = devm_ioremap(...);
|
 x = alloc_netdev(...);
)
 ...
- if(NULL == x)
+ if(!x)
        S
Further we have used isomorphism characteristics of coccinelle to
indicate x == NULL and NULL == x are equivalent. This is done via
following iso script.

Expression
@ is_null @ expression X; @@
X == NULL <=> NULL == X

Signed-off-by: Somya Anand <somyaanand214@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/trigger/iio-trig-bfin-timer.c

@@ -183,7 +183,7 @@ static int iio_bfin_tmr_trigger_probe(struct platform_device *pdev)
 	int ret;
 
 	st = devm_kzalloc(&pdev->dev, sizeof(*st), GFP_KERNEL);
-	if (st == NULL)
+	if (!st)
 		return -ENOMEM;
 
 	st->irq = platform_get_irq(pdev, 0);