greybus: fw-management: Fix 'make check' warnings

Fix below warnings observed with 'make check'.

~/ara/greybus/fw-management.c:438:33: warning: incorrect type in assignment (different base types)
~/ara/greybus/fw-management.c:438:33:    expected unsigned short [unsigned] [addressable] [assigned] [usertype] major
~/ara/greybus/fw-management.c:438:33:    got restricted __le16 [usertype] <noident>
~/ara/greybus/fw-management.c:439:33: warning: incorrect type in assignment (different base types)
~/ara/greybus/fw-management.c:439:33:    expected unsigned short [unsigned] [addressable] [assigned] [usertype] minor
~/ara/greybus/fw-management.c:439:33:    got restricted __le16 [usertype] <noident>

Reported-by: Greg Kroah-Hartman <gregkh@google.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>