usb: dwc2: Cleanup some checkpatch issues

This commmit is the result of running checkpatch --fix.

The results were verified for correctness. Some of the fixes result in
line over 80 char which we will fix manually later.

The following is a summary of what was done by checkpatch:
* Remove externs on function prototypes.
* Replace symbolic permissions with octal.
* Align code to open parens.
* Replace 'unsigned' with 'unsigned int'.
* Remove unneccessary blank lines.
* Add blank lines after declarations.
* Add spaces around operators.
* Remove unnecessary spaces after casts.
* Replace 'x == NULL' with '!x'.
* Replace kzalloc() with kcalloc().
* Concatenate multi-line strings.
* Use the BIT() macro.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>