nfp: Check resource mutex allocation

In the Linux kernel, the following vulnerability has been resolved: nfp: Check resource mutex allocation nfp_cpp_resource_find() allocates a CPP mutex handle for the matching resource-table entry and then reports success. nfp_resource_try_acquire() immediately passes that handle to nfp_cpp_mutex_trylock(). However, nfp_cpp_mutex_alloc() returns NULL on failure. If that happens for a matching table entry, the resource lookup still returns success and the following trylock dereferences a NULL mutex pointer while opening the resource. nfp_resource_acquire() already treats failure to allocate the table mutex as -ENOMEM. Do the same for the resource mutex and fail the lookup before publishing the rest of the resource handle. This issue was found by a static analysis checker and confirmed by manual source review.