test_firmware: use str_true_false() helper

test_firmware: use str_true_false() helper

Replace ternary (condition ?  "true" : "false") expressions with the
str_true_false() helper from string_choices.h.  This improves readability
by replacing the three-operand ternary with a single function call,
ensures consistent string output, and allows potential string
deduplication by the linker, resulting in a slightly smaller binary.

Link: https://lkml.kernel.org/r/20250814095033.244034-1-visitorckw@gmail.com
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>