mfd: kzalloc doesn't return ERR_PTR

Use !x rather than IS_ERR(x) to test the result of kzalloc.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression x,E;
@@

x = \(kmalloc\|kzalloc\|kcalloc\)(...)
... when != x = E
- IS_ERR(x)
+ !x
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>