usb: dwc3: gadget: increase readability of dwc3_gadget_init_endpoints()

The commit 47d3946e



	usb: dwc3: refactor gadget endpoint count calculation

refactored dwc3_gadget_init_endpoints() and in particular changed in or
out endpoint numbering to be through. It's not always convenient and
makes code a slightly harder to read.

Introduce a new temporary variable to make it easier to understand what
is going on inside the function.

While doing that, rename local variables as follows:
	u8 num	-> u8 total
	int num -> int kbytes

Replace implicit direction check via epnum with explicit use of
direction variable.

While here, replace %d to %u when compounding endpoint name since we are
using unsigned type.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>