xfs: xfs_trans_read_buf() should return an error on failure
xfs: xfs_trans_read_buf() should return an error on failure

When inside a transaction and we fail to read a buffer,
xfs_trans_read_buf returns a null buffer pointer and no error.
xfs_do_da_buf() checks the error return, but not the buffer, and as
a result this read failure condition causes a panic when it attempts
to dereference the non-existant buffer.

Make xfs_trans_read_buf() return the same error for this situation
regardless of whether it is in a transaction or not. This means
every caller does not need to check both the error return and the
buffer before proceeding to use the buffer.

Signed-off-by: Dave Chinner <4d9e23a041ac966f5316a7481300d4ae12e806fe@redhat.com>
Reviewed-by: Alex Elder <f556392d917047d964350b9c68912016c96d5e94@sgi.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas