Staging: dwc2: Fix variable dereferenced before check

This patch fixes the following smatch warning in hcd_intr.c-
drivers/staging/dwc2/hcd_intr.c:1946 dwc2_hc_n_intr() warn: variable dereferenced before check 'chan' (see line 1936)

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>