usb: gadget: net2272: remove redundant assignments to pointer 's'

The pointer 's' is being assigned however the pointer is
never used with either of these values before it it reassigned much
later on.  I suspect it was going to be used in the output of the
main control registers scnprintf but was omitted.  The assignments
of 's' to the driver name or the literal string are redundant and
can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>