usb: dwc2: gadget: Remove assigned but never used 'maxsize'

usb: dwc2: gadget: Remove assigned but never used 'maxsize'

The value of 'maxsize' has not been checked since commit 729cac693eecf
("usb: dwc2: Change ISOC DDMA flow") back in 2018, so remove the set but
unused variable, which fixes the following W=1 kernel build warning:

 drivers/usb/dwc2/gadget.c: In function ‘dwc2_gadget_fill_isoc_desc’:
 drivers/usb/dwc2/gadget.c:885:6: warning: variable ‘maxsize’ set but not used [-Wunused-but-set-variable]
 885 | u32 maxsize = 0;
 | ^~~~~~~

Cc: Minas Harutyunyan <hminas@synopsys.com>
Cc: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200702144625.2533530-11-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>