tools/csr_usb: Fix compilation failure

tools/csr_usb: Fix compilation failure

GCC's "format-nonliteral" security check is enabled as an error in
recent versions of Fedora. Given the limited formats, pass a boolean
to switch between the 2 different formats.

tools/csr_usb.c: In function 'read_value':
tools/csr_usb.c:82:2: error: format not a string literal, argument types not checked [-Werror=format-nonliteral]
  n = fscanf(file, format, &value);
  ^

Change-Id: Ia0c8d0c4bb77d472afa39a148aff41f220818571
Signed-off-by: himanshu <h.himanshu@samsung.com>