tpmevlogdump: clean up some minor cppcheck style warnings

Reduce the scope of some variables. Cleans up the following
cppcheck style warnings:

src/tpm/tpmevlogdump/tpmevlogdump.c:377:8: style: The scope
of the variable 'str_info' can be reduced. [variableScope]
 char *str_info;

src/tpm/tpmevlogdump/tpmevlogdump.c:471:13: style: The scope
of the variable 'data' can be reduced. [variableScope]
 uint8_t *data;

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Alex Hung <alex.hung@canonical.com>
Acked-by: Ivan Hu <ivan.hu@canonical.com>