media: mali-c55: Fix possible ERR_PTR in enable_streams

In the Linux kernel, the following vulnerability has been resolved: media: mali-c55: Fix possible ERR_PTR in enable_streams The media_pad_remote_pad_unique() function returns either a valid pointer or an ERR_PTR() on failure (-ENOTUNIQ if multiple links are enabled, -ENOLINK if no connected pad is found). The return value was assigned directly to isp->remote_src and dereferenced in the next line without checking for errors, which could lead to an ERR_PTR dereference. Add proper error checking with IS_ERR() before dereferencing the pointer. Also set isp->remote_src to NULL on error to maintain consistency with other error paths in the function.