libfec: fix a check for read-only mode

O_RDONLY is defined as zero, which makes the test for it incorrect. As
we don't allow O_WRONLY when opening files, it's sufficient to test for
O_RDWR instead.

Bug: 112147169
Test: tested that corrupt zero blocks are not read without O_RDWR
Change-Id: I2328cda4285f4c9daf98dffa2a6602c9db5ad539
1 file changed