coverity: debugfs devfip remove comparisons to LONG_MAX

CID 353228:  Integer handling issues  (CONSTANT_EXPRESSION_RESULT)

The checks on size and offset_address in get_entry always resolve to
false provided those fields are long long int and cannot be greater
than LONG_MAX.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I0fac485a39ac4a40ae8c0d25a706ad74c795e130