cmd: bcb: change strcmp() usage style in the do_bcb_ab_select()

cmd: bcb: change strcmp() usage style in the do_bcb_ab_select()

In the entire cmd/bcb.c file, the return value of strcmp() is not
directly compared to 0. Therefore, it would be better to maintain this
style in the new do_bcb_ab_select() function as well.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # vim3_android
Link: https://lore.kernel.org/r/20241017-android_ab_master-v5-4-43bfcc096d95@salutedevices.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>