selftests/alsa: Fix circular dependency involving global-timer

selftests/alsa: Fix circular dependency involving global-timer

The pattern rule `$(OUTPUT)/%: %.c` inadvertently included a circular
dependency on the global-timer target due to its inclusion in
$(TEST_GEN_PROGS_EXTENDED). This resulted in a circular dependency
warning during the build process.

To resolve this, the dependency on $(TEST_GEN_PROGS_EXTENDED) has been
replaced with an explicit dependency on $(OUTPUT)/libatest.so. This change
ensures that libatest.so is built before any other targets that require it,
without creating a circular dependency.

This fix addresses the following warning:

make[4]: Entering directory 'tools/testing/selftests/alsa'
make[4]: Circular default_modconfig/kselftest/alsa/global-timer <- default_modconfig/kselftest/alsa/global-timer dependency dropped.
make[4]: Nothing to be done for 'all'.
make[4]: Leaving directory 'tools/testing/selftests/alsa'

Cc: Mark Brown <broonie@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Link: https://patch.msgid.link/20241218025931.914164-1-lizhijian@fujitsu.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>