qemu_driver.c: Coverity fix in qemuNodeDeviceDetachFlags()

qemu_driver.c: Coverity fix in qemuNodeDeviceDetachFlags()

Commit 76f47889326c4 made qemuNodeDeviceDetachFlags() unusable due to an
'if then else if' chain that will always results in a 'return -1',
regardless of 'driverName' input.

Found by Coverity.

Fixes: 76f47889326c45d2732711bc6dd5751aaf6e5194
Reported-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>