usb: gadget: dwc3: Improve interrupt handler performance

Remove a costly dbg_print call in the interrupt handler.
From tests made, removing this logging save 7% cpu idle in heavy
load throughput scenario (50Mbps UL and 300Mbps DL)

Also, this debug print is not really add value for debugging,
instead one may use /proc/interrupts.

Change-Id: Iceb70e323ee7113d144dd5f7b99a2b126a4b3d76
Signed-off-by: Ido Shayevitz <idos@codeaurora.org>