tpm/tpm_ppi: Do not compare strcmp(a,b) == -1

commit 747d35bd9bb4ae6bd74b19baa5bbe32f3e0cee11 upstream.

Depending on the implementation strcmp might return the difference between
two strings not only -1,0,1 consequently
 if (strcmp (a,b) == -1)
might lead to taking the wrong branch

-> compare with < 0  instead,
which in any case is more canonical.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>