selftests: tpm2: test_smoke: use POSIX-conformant expression operator

Use POSIX-conformant expression operator symbol '='.

The use of the non POSIX-conformant symbol '==' would work
in bash, but not in sh where the unexpected operator error
would result in test_smoke.sh being skipped.

Instead of changing the shebang to use bash, which may not be
available on all systems, use the POSIX-conformant expression
symbol '=' to test for equality.

Without this patch:
===================
# make -j8 TARGETS=tpm2 kselftest
# selftests: tpm2: test_smoke.sh
# ./test_smoke.sh: 9: [: 2: unexpected operator
ok 1 selftests: tpm2: test_smoke.sh # SKIP

With this patch:
================
# make -j8 TARGETS=tpm2 kselftest
# selftests: tpm2: test_smoke.sh
# Ran 9 tests in 9.236s
ok 1 selftests: tpm2: test_smoke.sh

Link: https://lore.kernel.org/r/37ztyakgrrtgvec344mg7mspchwjpxxtsprtjidso3pwkmm4f4@awsa5mzgqmtb
Signed-off-by: Ahmed Salem <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/tpm2/test_smoke.sh

···
 
 [ -e /dev/tpm0 ] || exit $ksft_skip
 read tpm_version < /sys/class/tpm/tpm0/tpm_version_major
-[ "$tpm_version" == 2 ] || exit $ksft_skip
+[ "$tpm_version" = 2 ] || exit $ksft_skip
 
 python3 -m unittest -v tpm2_tests.SmokeTest 2>&1